Boy, I like my Tablet PC, but I don't know if I would recommend switching from a desktop because of the speed you get with even a "half old" machine.
If you're looking for mobility, then I would say "go for it," however.
I'm no pro, but I've worked with art programs on the Tablet and I like them. I've seen what pros can do with the Tablet, and I am impressed.
I have no idea about tilt on the Tablet pen, however. I don't remember seeing any mention of it in the Wacom drivers for Tablet PCs.