Skepticism is a healthy attribute. And to be brutally honest, of course Bitcoin is likely to fail - all new things are likely to fail. We're all engaged in a wildly speculative and risky venture, here. Even conservative ventures usually fail, and this is anything but conservative.
I agree with you on most of what you say: Bitcoin is a technical marvel, and it's shown by example how to set up a distributed currency system. I would love to see the day when I can send money internationally instantly and without an intermediary / enormous fees. I'm learning everything I can about the technical aspects of Bitcoin and am hoping to contribute back to the community in due time to bring its vision to fruition.
But I think what will ultimately happen is that the original Bitcoin will fail and a successor to it with saner economics will take over it. At the risk of igniting the wrath of others on this forum (as I've seen happen elsewhere, even in this post to a partial extent), the fact that Bitcoin is deflationary will, I think, ultimately be its undoing:
* I don't see how, in the long run, a large number of people will spontaneously show the altruism necessary to get past the hoarding mentality of "why should I buy this today when I can buy twice of it tomorrow". If everybody hoards their Bitcoins, merchants have no customers. This is essentially a tragedy of the commons: everyone knows this will be a tragedy, and everyone hopes that there will be a vibrant Bitcoin economy, but the incentives at the individual level are set up so that you participate in that economy as little as possible while hoping that others won't do what you do. We all know from experience that in these situations, it's the commons that yields, not the individuals. Bitcoin attracts lots of "free market" people that loudly point out the importance of the word "free", but you can't spell "free market" without the word "market".
Hoarding bitcoins is not a problem. There are plenty of units to go around even if everyone hoards. Hoarding merely increases the value of bitcoins.
* I don't see how any kind of lending will work well (operative keyword: well) in the Bitcoin world. Put yourself in the mentality of 100 years into the future when everyone earns BTCs and can buy anything with BTCs. Now, if I lend you money, I will reasonably ask you to pay me back more than what I gave you; otherwise, I might as well have kept my money and not run the risk that you'd default on the loan. But with every passing month, it becomes harder and harder for you to pay back the loan, as your salary drops and drops every day. Now imagine something wonderful happens: I don't know, the Internet gets invented and millions of new jobs get created, so the economy expands, and so your paycheck goes *way* down. Your debt hasn't, and you're screwed, even though things were supposed to have gotten better, not worse. In an inflationary system, banks get screwed if the inflation rate goes way up (and they marshall the resources to fight this possibility hard), but banks are much better at coping with large economic shocks than are individuals with relatively tiny savings.
Lending will be less common in the bitcoin economy, but this isn't a problem. The fact that lending is so common with fiat currency systems is because banks create most of the money out of thin air and give it to themselves, and thus if you need money you have to get it from a bank. So lending is artificially high with fiat currencies because the central banks and their banking cartels have a monopoly on the money. Lending will be back to normal levels with bitcoin.
In a spirit diametrically opposite to what Bitcoin is supposedly setting out to do, I can't think of a better way of transferring enormous amounts of power to a small clique of bankers than deflationary lending. All these people have to do is lend out money, charge interest, and never do anything with that money. So either people aren't going to borrow money (good luck buying a house with your savings before you're 50 if you're in the bottom 98% income bracket), or we get enormous concentrations of power in lenders. Neither of these prospects is appealing, and if the community's answer to these problems is to pretend that they don't exist, then by and large, the outside world's reaction to Bitcoins will be to pretend that they don't exist.
* By the way, try convincing anyone that its fine for their *nominal* paycheck to go down and down as they work more and more. I think human psychology will trump the rational explanation that the amount of stuff you can buy with your ever-decreasing paycheck remains constant or increases. Look at how many gimmicks companies today will go through to avoid cutting salaries during a recession, it's utterly demoralizing.
People will accept lower paychecks just like they accept rising prices today.
What I think might actually take off is a Bitcoin-like currency with a baked-in small, fixed rate of inflation, say 2% or so. This gets rid of the hoarding problem: you're better off investing your money in something productive than sitting on it indefinitely. It gets rid of the initial distribution problem by inflating away the "hard-earned" savings of the early adopters that stop contributing to the community after a few months of "back-breaking" mining, without undermining the savings of those who invested in furthering the Bitcoin ecosystem (my understanding is that some early adopters hold double-digit percentages of the whole Bitcoin economy, which puts it on par with Zimbabwe's wealth distribution). It lays down the foundational for a sustainable banking system, where there's actually an incentive to lend money that would otherwise sit idle. There's no central banker pulling the levers to control the inflation rate or to benefit from its control, if that's the bug that keeps you awake at night (see OP's last few replies), so it's not central-planning [off-topic, just thought I'd mention that there's a wide spectrum of economic possibilities from deflation to authoritarian central planning, and it's a stretch to claim that guiding macroeconomic policy with a single, blunt lever is equal to authoritarian central planning].
No one will want to put their money in an a currency that is just like bitcoin except its value drops with time.
The way I imagine this playing out is that Bitcoin eventually forks into separate currencies, and the mildly inflationary variants are the ones that actually gather mass momentum, leaving the deflationary variants in the dust (with their hoarders' fortunes not having lost a cent of nominal value, but becoming ultimately worthless). Mild inflation, not subject to political influence, is a fair and equitable way of incentivizing economic activity and investment.
I know many of these things have been said before, but I think it's important to keep them in the day-to-day discussion. The community hasn't come to a consensus that deflation economics is great (I get the sense there's a collective delusion that it has), and to me, that's the point that seems most likely to end Bitcoins as it exists today. My optimism, which I share with the OP, is that the underlying technology is marvelous and the fundamental idea of Bitcoin is sound, so I expect those portions of the experiment to outlive Bitcoin itself.
). 
