The Treo is very mac friendly. I agree with the previous poster - Missing Sync offers an added level of features not found with the included HotSync manager. I wouldn't expect too much support from Sprint or any of the wireless stores. In their defense, they have plenty of phones and the Treo is a "smartphone". I wouldn't expect them to know the ins and outs. As a Mac user, I'm sure you're used to the "blank stares" when you ask if a product is mac compatible. I had FIOS installed the other day and the installer looked at my Powerbook as if it were from another planet. He then asked me to launch Sahara.
Take the leap and get yourself a Treo - if you run into problems, there are many willing mac users who will offer to help out.
-Chris