In order to get full compatibility with iCloud, we have to change our database from sqlite to core data. The danger of doing that is data loss on update. So we’re really spending our time on bug testing making sure data loss doesn’t occur… as that is literally the worst possible thing that could happen in our app (aside from iconcal somehow turning your iPhone into an atom bomb).
So that’s why 2.1 is taking so long. Hopefully we can get all of that ironed out. But there is always a chance that there is something that slips through the cracks and we don’t catch. It is ALWAYS a good idea to backup your device via iTunes (actually backing it up, not syncing it: http://support.apple.com/kb/HT1766). This is a good practice before updating any app where you store important data, as iOS’s update system isn’t flawless (like all technology - don’t hate me Apple).