What's all this have to do with poker? So far, not much, but an opportunity is there. People post about whatever is important to them, and for a lot of people, it's poker. Many of the Twitterers I follow post about poker--wins, losses, quotes, short anecdotes and quick tips. It's fun and insightful to take part in. Try to search Twitter for the word "poker" to get an overview of the on-line poker scene and find new folk to follow.
There is also a use for Twitter in covering live events. Many tech conventions have already taken advantage of it and I see no reason why poker events would be any different. Since you can post from your mobile phone, players can let the world know when they busted out or where Dolye Brunson is signing autographs from the WSOP. TwitterYourPoker.com is starting to organize that endevor. As phones start to use GPS location to tag "tweets" with coordinates, this will become even more useful.
If you join Twitter be sure to follow me and let my know that you read Hell's Cold Day by sending me a message by starting your post @grundy.