I agree. Tweet-a-beer (especially for a local brewery) has more of a community feel. Tweet-a-coffee (even though I end up at starbucks almost daily) feels more like giving to a faceless corporation.
Its not my area, so I don't know how easy it is to do, but I do think it could be a space for a third-party to step in. Someone figures out how to handle the twitter/payment side, reaches out to some local breweries/bars, takes a small cut of the money for each beer tweeted. Its not going to be a super profitable business, but it might be a fun sideproject for someone.
I forgot to add the 3rd benefit to the brewery is that I would assume, in general, when people stop in, they don't come alone, and they don't just have one beer and leave. Once they're in the door, they tend to spend more money.
Well, sure, they'd get business--that's the benefit.
But how easy is it to tie into twitter and a payment system? That'd be the cost.
Starbucks can distribute such costs (which may not be fixed, but certainly won't grow linearly) across a larger number of stores than your local brewhouse can.
While there may be issues with localized liquor laws, this is the greatest idea I've ever heard. Too bad you just missed the last YC batch! I'd be your first beta user.