Part of the reason that I held onto my .mac address for so long was the syncing abilities. I was working from a Powerbook and an iMac and it was nice to jump back and forth without missing a beat. But recently I chose not to renew .mac because a) Gmail just offers so many options and is free, b) the IMAP syncing was making Mail.app lock up and c) I found MySync.
MySync provides the Mac-to-Mac syncing capabilities of .mac, without .mac. There are all kinds of great options to choose from.
MySync is free for now, but will gain a price at some point. Get it while the getting is good.