If you are one of those unlucky people who still don’t have IMAP support (and other neat brand new features) in GMail, try to change you language to US English. For me, it did the trick in every account I own that were not in english.
Switching back to your preferred language, downgrades the Gmail version as well, what a pity… well, I think it’s only a question of time. Meanwhile, if IMAP support is vital for you, this works quite well.
The eternal fight between admins and computers 
I found that after switching to US English and logging in to IMAP, that IMAP continues to work even after you switch Gmail back to your original preferred language. Might want to give that a try.
yes it looks like the servers that serve US english have IMAP support but others do not. this does not really matter if you switch to IMAP for your primary access but is a pain none the less. I am not sure about the build out but hopefully they will do the spanish next
@wg: I was supposing this but thank you for confirming it