Right, but the review did say that this one does at least try to run in the background. However, I do have to agree with the review, and say that it crashes, A LOT, which sucks. MobileChat is another application that works a ton better, though it doesn't support background operation (if I remember correctly). It looks a lot nicer, with the conversation view looking really nice like the SMS app.
Version 3.0 of this app is scheduled to come out with the 2.0 firmware release over the Apple Store. You can read more about it here:
http://tumblr.twenty08.com/
Update: I reread their page, and it seems like it will have some sort of queuing mechanism to let you still get messages when not connected to the net/in sleep mode:
http://tumblr.twenty08.com/post/3556...t-and-re-built