I had severe issues too with the Mac app too, like lost email drafts. The problem is that email is difficult to handle. Sparrow does an excellent job with the UI and while that part was ready for a 1.0 release the email handling was not. It takes a lot of manual testing due to the way other email applications and servers abuses email standards. They released it to early for it to be labeled stable IMHO. The current release is decent though, but still found bugs and it has been a while since the latest update (they must have put all resources on the iPhone-app). Hopefully they haven't done the same mistakes with the iPhone-app. Looks great with my limited testing so far and I have replaced my main Mail-icon on my home screen.