Google is selectively rolling out IMAP for Gmail. One of my accounts was lucky to get it and I'm testing it now. I have written to Google begging for this many times and I've even signed online petitions. So yeah, I'm really excited about this.
Until now, my email setup consisted of Gmail for domains and my own IMAP server that I setup Gmail to forward all mail to. Then I setup Mail.app to read mail from my IMAP server but to send using Google's SMTP server. I did all that so that I could read mail using Mail.app in multiple computers, multiple OS installations, as well as the iPhone while still having it all archived in Gmail.
I'm so glad that I can do away with this fugly work around.
It's great seeing the folders I create in Mail.app show up on Gmail's web interface and vice versa. This means that Gmail's web interface is now 10 times more useful to me. I may actually even use it.
Christmas came early for me this year.
On a separate topic, work on my new application is progressing nicely. It's still too far away from release to say anything more, but things are looking pretty sweet.