The new iPhone firmware (1.1.3) came out today. While I generally applaud the new features (although the faux gps can frequently provide highly dubious results - many miles off course), I luckily ran across a notice of one key change which is easily overlooked.
Gmail accounts which were set up to use POP will be automatically switched over the IMAP. This seemingly obscure technical detail means that users who are used to deleting messages harmlessly on their phone, are now also deleting the originals on Gmail.
Luckily I found this out before doing any irreversible damage, and recovered the files from my Gmail trash. For more info, check out this tech note from Google.