You guys can blast the OP all you want, but he does have some valid points. In my opinion, the biggest weakness of bitcoin from the consumer standpoint is one simple thing: consumer protections. Or rather, the lack thereof.
A few people mentioned credit cards and being worried about their numbers being stolen online or at some merchant etc. I personally don't worry about this happening ever. Because I know that if my card information is stolen, I have $0 liability for transactions. My bank can invalidate the old card and issue me a new one. It is because of this that I feel confident shopping online with my credit card at merchants that I know nothing about, knowing that I can perform a charge back if they decide not to deliver the product they claim to be selling.
None of these protections exist with bitcoins. With bitcoin, you really only want to use it on trustworthy sites like Overstock, because if you're using it on Joe's Music Store, where you've never transacted with Joe before and know nothing about him, you could get some great new CD / set of MP3s. Or you could be throwing away $20.
But there are a few natural markets for bitcoin, of course. Some people have already mentioned porn and drugs, these are both big ones. The porn industry has a huge problem with chargebacks from people who bought porn and then later didn't want to admit it so it's really in their best interest to not only accept bitcoin, but possibly go bitcoin only eventually.
The other less controversial market is of course remittances. Remittances is a huge market, there were around
$53.8 billion in remittances from the United States to Mexico and Latin American countries just in the last decade or so. The problem here is, as always, the exchange rate. With remittances, you're generally doing a person-to-person money transfer, so unless the person is waiting on the money and can get it one or two blocks later, there's a decent chance (especially these days) that the person on the receiving end would end up getting less money than was sent.
The big question there is this: is the potential loss greater than the amount of money Western Union charges to do currency conversions? Their fees aren't cheap if you're sending a lot of money, so it could very well be a loss or even in bitcoin's favor.