I have a Wacom CTE-640. While I don't use it for astro stuff, I do use it for other photo processing. It absolutely rocks for fiddly bits when the mouse just isn't accurate enough (masking, etc).
The thing I find most "annoying" is the absolute positioning on the pallet... with a mouse you move it part way across the screen pick it up and move it back and have another go - and I've gotten used to that
, but with the pallette, the position on the pallette relates directly to the position on the screen so you just have to move the stylus all the way across - no being lazy!
It just takes a bit to get used to.
They are a great bit of gear for what they are intended to do!
Al.