I use mine in SU.
It depends a bit how nerdy you want to be. If you're happy using the programmable ("soft") buttons etc. it can be really useful. I find the best combination is a good trackball - I also have one of these connected ("Kensington Expert Mouse", but I'm not sure if they're still around):
It's built like a tank and you can use it with any finger or thumb unlike some of the silly-shaped ones. The four buttons mirror the two mouse buttons (two of each), so there's always one easily reached.
Trackballs are unsurpassed for accurate positioning of the cursor, simply because you can take your fingers off it without anything moving. Position; leggo completely; click! So it's horses for courses - the pen is fast, the trackball is slow but precise. The two used together are unbeatable (IMHO).
The tablet+pen will let you trace fairly accurately through fairly thick paper (1/4" probably, depending on the material), so you can, if you wish, go over a drawing.
"Proper" Wacom pens have two buttons, plus the tip (you tap it), plus an "eraser" on the other end. Most button/tip combinations can be mapped to mouse functions, or text strings or whatever, and if you have the expensive ones you get extra programmable buttons on the tablet, and a scroll wheel with a button in the centre (it is touch sensitive. The tablets can detect the difference between the pen and fingers, too, so you can assign gestures, although personally I find that annoying and have it permanently turned off (I'm an old fogey).
In general use I find a pen/stylus about twice as fast as a mouse for most things and far less irritating to tendons, etc. That's a big reason for using one. You can set sensitivity (to taps and double taps, pen pressure for drawing, etc.), and tilt sensitivity - it recognises the angle the stylus is held at (if you want it to). That's great for freehand drawing but overkill for SketchUp, etc.
The size of the tablet I think matters quite a bit - too small and you can't be precise, too large and you're conducting an orchestra the whole time (and it gets in the way too). I'm happiest with an A5 active area, and my one annoyance with the current generation of Wacom tablets is the wasted "land" area round the edges - my really old one is just a pad with no extraneous styling. The old one also has a lift-up transparent pad so you can slip drawings or notes underneath (good home for Post-Its) - Wacom have dropped that feature too, which is a shame. I didn't think I would, but I do like the buttons along the side and the touch wheel. If you're a lefty, you probably want the buttons on the right and vice-versa, so the ability to flip the thing over (in the control panel/driver setup) is really handy. Mine can be cordless, but I've taken the battery out and use it on USB all the time, as I don't like fussing about with charging it. The socket is at the side, so being able to flip it physically is important.
All these pointing devices are very personal things - you need to find something that's comfy and you can use for long periods, and which gives you the control you need. I've got arthritis: if I do eight hours with a mouse my hand screams at me for hours afterwards (likewise with a #7 plane!). With a pen it doesn't and I'll have got more done, too.
Your mileage, etc.
E.
