I switched to push email yesterday and it works fine for me.
Add new account, click next, click provider, select "Nokia Messaging" and enter your account details...

I have three IMAP-accounts, my workmate had one gmail-account, but the added "Nokia Messaging"-account did not appear
and therefore no push email, any suggestions?

Push mail is really great, because mails will be pushed almost instanteneously to your N900, instead polling them every 30 mins or so.

Edit:After adding "Nokia Messaging", disable "Automatic Update"