I have been using the beta version mobipocket reader for the past few days and have not had any problems with it. I was using the old version and it was usable, but barely. They have made several excellent upgrades for the Storm and it seems to be working just fine. Once you download it you need to pull the battery and perform a hard reboot, make sure the compatability mode is disabled, and it should work.
"When everything seems to be going against you, remember that the airplane takes off against the wind, not with it." -Henry T. Ford