Nice try. In July Twitter wrote that it was trying to trademark "Tweet." Not for the reason you might think, though: the request has been provisionally denied on the grounds that other companies had filed for trademarks of very similar words.
You might think that "Tweet" was a generic term, and that would be the reason for the denial, but the U.S. Patent and Trademark Office (USPTO) cited other trademark applications by the firms TweetMarks, Cotweet and Tweetphoto, and said there was a "likelihood of confusion."
In his blog post announcing that Twitter was attempting to trademark "Tweet," founder Biz Stone said he wasn't concerned with other firms, such as the above, who are using Tweet in their names:
There are lots of really awesome services and applications out there like TweetDeck, TweetMeme, Tweetie, BackTweets, Tweetboard, and others that we absolutely love as do many users. However, as the ecosystem grows there is also the possibility that confusing and potentially damaging projects could emerge.
We have applied to trademark Tweet because it is clearly attached to Twitter from a brand perspective but we have no intention of "going after" the wonderful applications and services that use the word in their name when associated with Twitter. In fact, we encourage the use of the word Tweet. However, if we come across a confusing or damaging project, the recourse to act responsibly to protect both users and our brand is important.
It appears, however, that Twitter was simply too slow. Ironic, as their logo includes a bird, but "the early bird gets the trademark."