Turns out I had it set up wrong. The developer suggested uninstalling and using the Gmail settings (rather than IMAP) to sync my account. This seems to be working fine.
Just another data point: I've been testing a pre-release version of reMail for the last month without any real problems or crashes. My setup: gmail (not IMAP), iPhone 3G, 3.0 OS.
After reinstalling and reconfiguring, search and display of emails works fine but the app crashes after about every 50 emails it syncs.