I’ve used .mac and most of the other services you mention for quite a while. Where .mac really shines is when you have multiple computers running OS X. My assistant and I share the same address book (which we could do with Plaxo), but I can also take a peak at her screen from my computer anywhere in the world using Back to my Mac. In the same way I can connect to her hard drive and vice versa.

For me the .mac account is well worth the small expense–even if I could get similar functionality for free using a bunch of other components. The easy of use is hard to beat and having a reliable system is worth quite a bit.