After giving more storage for its Gmail users (I have 4 Gb of storage right now), Google starts to give IMAP support. Google Help Center already mentioned about Supported IMAP Client List. But it seems that not all accounts got this feature. I checked both in my Gmail and Google Apps, I still haven’t got the options to enable the IMAP settings, only POP.
Why is IMAP integration a good thing for Gmail?

POP was a stepping stone, but IMAP pushes Gmails benefits over the top. With IMAP, users can now access their email via a desktop application like Outlook or Thunderbird, read emails, make changes, delete, and have the changes made across platforms. So if you now log into your Gmail account, the message which you read in Thunderbird, will now be marked accordingly. No more wasting time trying to sift through emails that had already been answered. (source)

Okey, I’ll wait.