I just paid way too much money for an iPod touch (because I’m a technoslut), and in playing around with the Mail application it comes with ever since Macworld and the “free Software Upgrade”, I noticed a bit of a gotcha while using GMail IMAP accounts.
It seems, that despite syncing up with my iMac’s accounts, the iPod touch (and, presumably, the iPhone as well), treat the “Trash” mailbox specially. Specifically, whereas you can map the “Delete” button in Apple Mail.app to function as though it were the GMail “Archive” button (by following these simple steps), Mail on the iPod touch or iPhone won’t inherit the same behavior. “Delete” on the iPod touch really is an honest-to-goodness delete—forever.
Instead, to Archive GMail messages on an iPod touch or iPhone, you’ll need to tap the “Move” button (the folder icon with a downwards-facing arrow, second from the left on the bottom toolbar) and select the “All Mail” folder. I wonder why the difference in interface choices….