IMAP IDLE command, server side filters - questions

I use Thunderbird (3.0 nightly builds) to access MS Exchange 2007 email using IMAP. I've enabled the use of IDLE command so that the server tells Thunderbird when I get an email. However, I don't think it is effective enough. From reading about IMAP and the IDLE command, I have a few questions, may be someone can help me:

1. Does MS Exchange 2007 support the IDLE command the way Thunderbird likes it?

2. Is it true that the server 'pushes' only the email messages in the INBOX? If I have server side filters that move messages into folders upon arrival (which I do, a lot), do I still need to poll the server for those folders?

3. If I enable IDLE command in Thunderbird, and check the 'Check for new messages every N minutes' option, is it just redundant, or does it disable the use of IDLE command?