Calendar, Tasks, and Contacts DON'T work seamlessly with any device OTHER than the iPhone. There are solutions out there that enable you to have the same information in all places (I use the Blackberry), but none that allow a completely mobile experience.
You can't send mail "From" accounts that don't have a .mac, or .me domain . If you have a business e-mail address, this kind of sucks. I'm not sure WHY apple's service is the ONLY major service out there that won't allow this, but I'm sure they'd attract far more consumers if they did.