Supposedly, savings for merchants can get passed on to customers. For example, I have heard that prices on bitcoinstore.com (which is a big consumer electronics site) are significantly cheaper than elsewhere. I haven't tried to compute that myself, so I don't know if it's actually true.
Also, when paying with Bitcoin, I don't have to reveal my name to the merchant. That can matter a lot for certain things. For example, I wouldn't want to make any kind of "adult" purchases using my real name.
Bingo! Adult websites have been technological pioneers and they can probably help drive Bitcoin forward with payments. I think it's the most promising method of getting bitcoin into the mainstream.
Also, when paying with Bitcoin, I don't have to reveal my name to the merchant. That can matter a lot for certain things. For example, I wouldn't want to make any kind of "adult" purchases using my real name.