I've finally got GMail on Apple's Mail.app, so I can check my GMail remotely. Even better, if I had some form of portable communicator device (no, I'm not in the queue already) then I'd be able to use my GMail from that, too.
It takes a bit of convincing to enable IMAP. You need to turn on the 'hidden propery' on the settings page; in fact, it turns out that it's only enabled for US translactions at the moment. So,I switched the appearance of GMail to use English (US) instead of English (UK), saved the changes, logged out and back in again - and the mysterious setting appeared! You need to save the changes after enabling it (and it takes a few seconds in my experince to get going) but then you can configure Apple's mail client (courtesy of these instructions) and (after getting your password right on the second attempt) you get to use GMail!
Once your account is set up and synchronized, you can select the [GMail]-Drafts folder, go to the Mailbox menu, and then "Use this Mailbox for - Drafts" to configure it to turn up in the right place. The same is also true of the spam folder, trash, drafts etc.
The settings are
smtp.gmail.com:587. Both use SSL and both use your GMail userid/password for authentication.