I recently posted on how to get started using Twitter for your winery. Now John Jantsch of Duct Tape Marketing has created a free e-book called Twitter for Business which will help you take the next steps to using Twitter to meet specific marketing goals (which he lists).
In particular, I'd like to mention his coverage of the Twitter search feature, which allow you to see when people mention your winery on Twitter (much like having a Google Alert for your winery name). Other companies such as Dell and Comcast are already doing this (I tweeted "I hate Comcast" one day, and got an immediate response from Comcast customer care asking what they could do to help).
Note that to get maximum effect from Twitter search, you'll want to know how to subscribe to its feed (as always, I recommend using Bloglines or the feed reader built into IE 7 or Firefox 3).