If you're anything like me, for the past few days you've been checking the settings page of your Gmail/Google Apps Gmail account hoping to see an IMAP settings page. Google is slowly rolling out free IMAP access to all Gmail accounts. This is huge. IMAP support has generally been ignored by free email providers for the extra server resources and bandwidth required by IMAP access. The IMAP protocol stores everything on the server so regardless of which device or computer you check your email from, any changes are global.
Ever since I got a Gmail account on June 29th, 2004 (and subsequently my Google Apps Premier account) I have been using the web interface. I am an adamant labels user and with POP3 access, it was not possible to view labels as folders. With IMAP, your labels show up as folders in your mail client of choice. The only drawback of using a mail client instead of the Gmail web interface is you lose the message conversation view (that is, email threads are grouped as one "conversation").
This is such big news for me that I might even buy an iPhone this weekend to take advantage of it. The Gmail mobile app on the BlackBerry is only so good.
Is IMAP enabled on your Gmail account yet? If you do have IMAP enabled and are having trouble setting it up on your iPhone or Mail.app, Derek Punsalan has a great tutorial.