I have my INBOX Sync set to all. But I manage my inbox in a way that only my latest 20 or 30 e-mails are there. Anything that is done is moved to an archive folder, or deleted. I do sync other folders as well, but they're just a inbox sorted by subject - Inbox for Geekzone, Inbox for Personal, Inbox for Work...
I've seen users with 8000 e-mails in the inbox! The person never delete anything because she didn't know how to move to other folders. Lucky she didn't have a Pocket PC too :P
Have a look here:
http://www.goodexperience.com/reports/e-mail for some good suggestions. I think I'll post an article about this...