Well. My tablet arrived this morning, and I have to say it's quite fun.
It's the Graphire4 XL (A5)
First impressions: It's very thin. For some reason, I expected it to be deeper, but it's about 1cm at the front edge, up to about 1.5 cm at its thickest. The pen is light, with a rubber grip, and two buttons on the side.
Installation: Very easy, just installed drivers and started using it. No need for even a reboot.
Customisation: Pretty easy. I have the two pen buttons set to CTRL+Z (undo) and F6 (new keyframe), I haven't done anything with the actual pad buttons or scrollwheel yet.
Use: The weirdest thing is the fact that you have to move your hand a fair distance to go across the screen. I have my mouse set on high speed, so it only requires about 3.5 inches of movement, whereas the tablet requires you to move the full width of the active area (8 inches in the case of this tablet).
Apart from that, it's fairly straightforward. Lift the pen slightly to move without drawing, put it on the pad to draw. In Flash, two new options have appeared under the brush menu, PRESSURE and TILT. Pressure means basically that your lines will get thicker and thinner as you stroke and press, which gives a much more realistic style. I didn't enable tilt, but I assume it does a similar thing depending on the angle of pen to tablet.
People (myself included) assume that the tablet is there JUST for drawing, but it would actually be entirely possible to use the pen & tablet to completely replace your mouse - ie, use just the tablet for all navigation of your PC. Personally, I prefer to use the mouse for non-drawing, but the option is there.
In terms of drawing, getting the feel of the amount of pressure to apply takes a few minutes, but from there it's pretty natural. I daresay it'll take a while to master - I spent about 40 minutes drawing this tree (as you can see, I'm not the best ever artist...)
All in all, a good buy, I reckon I'll be using this a fair amount in Flash.