Hi, this is my first post here. I just installed Fission 2.5.5, and it seems to be buggy... I had both the welcome screen and the app market Force Close on me. The biggest problem, though, is that the Dialer app seems to be missing!
EDIT: I just wanted to mention that I'm on a Droid R2-D2 that has been flashed to 2.3.20. Fission 2.4.3 was working very well just before I installed 2.5.5.
As Trook said, they rolled out a bugfix shortly after the initial release. (That's why I said I thought my initial download was corrupted -- FRM insisted that my ROM wasn't current.) Fission 2.5.5 works like a charm for me now!