1. It's not possible to search your e-mail.
2. It's not possible to directly copy & paste from e-mails (although it's possible with a work-around).
3. No push e-mail for Gmail yet.
4. IIRC no threaded e-mail conversations (shrug). I love Google's way of grouping replies together one topic, it's very easy to reread all has been said about one e-mail topic. Instead of looking up eveyr individual e-mail reply in a long list.
5.No portrait mode for easy/quick viewing of e-mails.

If you need real good e-mail functions, I would recommend a Blackberry or Motorola Droid at the moment; and check back in 6 months to see if Maemo/3rd party apps have been improved for the N900.

Also check out this review about the N900's email functionality.

http://thenokiablog.com/2009/10/19/n...-review-email/

Basically the e-mail client is stuck in the 1990s. It's not very sophisticated.