I am not experienced with c++ (unfortunately), so that would be one reason I could not join ZeroReserve.
Not a very good reason for a Java programmer considering how similar Java and C++ are. Especially since there is a lot of Java to do. For example: Currently ZR uses the Satoshi client. But since this is a full Bitcoin node, I'd like to have bitcoinj as a drop in replacement. For this, someone needs to create a bitcoind compatible JSON-RPC layer like Mike Hearn proposed. Eventually there will be a Java implementation - we have to move to mobile platforms.
Another problem I personally have with ripple style concepts is the combination of friendship relationships with money. If I lend money from a friend and I am unable to pay it back, my friend can get in trouble as well and that could have influence to the friendship. All that can easily happen without any bad intention (accident, cannot work anymore,...). I prefer a system which is more abstract and handle those risky with insurance, like the banks are doing it. That does not imply that I am fan of Banks ;-)...
First, you would not necessarily grant your friend a credit that is anywhere near to the amount you trust him with. If a friend really cheats you for that smaller amount, that does influence the friendship, but in that case I'd say: Good riddance.
Another misconception is the meaning of "friend". In ZR context, it is simply someone you trust with money, for any reason. It is not the same as "close friend" or even "drinking buddy".
It is an argument I hear very often. Yet those same people trust a centralized exchange like MtGox or even btc-e. Does anyone know anything about btc-e? And why trust banks, especially today? Historically, banks screwed their customers every 5-7 decades. We Germans got screwed big time after WWII but we generally had the feeling like we deserved it for the war, so it went unnoticed. Now the system in the entire West is heading for another big reset.
Lastly, there is such a system that works since centuries, even millenia: Hawala / Hundi. Ripple is by no means a new idea. It is just that computer-less Hawala doesn't scale well while with computers it does because the software takes care about the complexities of routing. ZR enables everyone who chooses participate to become a Hawaladar. I think we need to walk away from the current banking system as much as possible.
The network effects you mention applies to every P2P system: The more people participate the more attractive it gets. There is the dilemma: 5 guys implementing 5 different system may result in the failure of all 5 systems because none of them ever achieves critical mass. If those same 5 guys had joined in a team to implement one, it may have succeeded. And: Given enough eye balls, all bugs are shallow (Eric Raymond)