Built-in Exchange support for real corporations is sorely lacking. Remote wipe and PIN locking are not supported. SSL causes problems with attachments in some situations. Most corporations (especially financial and medical) require privacy or HIPAA signatures - which are not supported by Android 2.0.
Apps like touchdown can fix some issues, but overall most serious IT depts are not going to like the droid.
I started this thread which has more info:
Exchange FAQ, Solutions, and summary
Also, at the bottom of the first post are links to google's issue tracker. Please visit each issue and mark it with a star to encourage google to focus on fixing exchange support!