The day has finally come for cloud-based rules in the MobileMe world :-)
I have been an iTools -> .Mac -> MobileMe user through the whole ride (starting the day after iTools was open for new users), and the service has had me wanting to leave for some time... and I still might in a year or two. However, server-side mail sorting rules (along with other new features of the online webmail client) are a huge boon for me:
Rules to keep your email organized everywhere. Mail rules help you reduce inbox clutter by automatically filing messages into folders you select ahead of time. Set them up at me.com, and your rules organize your incoming email on the web and everywhere else — on your iPhone, iPad, iPod touch, Mac, and PC.
One of the most annoying things about using my iPad as a laptop replacement is the fact that rules aren't applied to my emails. I get about 100-150 emails a day, and about 50 of them are sorted by rules (into archival folders, routed to the trash, etc.), and I don't want them marked as Junk.