I know that if you go into manage accounts, and view the properties of your IMAP mail account, you can specify wether to download the message bodies or not.
I think it was set to 'not' by default.

Mine did the same thing. It doesnt download bodies, but it does spend a bit of time talking to the server. Ill have to take a look at my IMAP server log and see what its doing.

Not sure how to set it to not check every folder when it looks for new mail. Setting this up would considerably shorten its connection time.
For example, I have no need to check my drafts, and Sent Items folder for new mail every time I check mail. New mail only goes into 1 of 7 folders. Yet, Opera likes to check all 7 just in case.
If anybody figures out how to do that please let me know. I have my OE set this way, and I think thats why it seems faster.