I think it would be great to offer a partial refund for not delivering Tweetie OR a complete refund for the entire bundle... Only problem, what to do with those who bought the bundle before the Tweetie announcement?
Only problem is that is a dumb idea. You DID get Tweetie, and you are still entitled to Tweetie 2 beta access when it becomes available. Furthermore, Loren has already said that all Tweetie license holders will get a free update to Tweetie 2, so you will be getting that, too.
Apparently what you do not and will not get is the fact that these programs are not just oozed right out but must in fact be written by someone. In this case, the someone is almost certainly working on several projects and has bosses to make happy. People are also waiting for Twitter for iPad, and it would not surprise me if that were a higher priority for Twitter and Loren than a beta for a Mac app.
avatar is from Penfield & Jasper, 1954