I found them only mildly useful but that's because I've learned how to draw better with a mouse. If you learned traditional drawing and rendering the tablet and pen will be MUCH more comfortable for you.
I sold mine because the pen grew more and more uncomfortable. Hence why I honed my skills on computers.
I've been thinking of getting one, for Maya and Photoshop. From what i've heard, Wacom is the way to go. The intuos2 is supposed to be the best bang for the buck, and the one in the link is supposed to be good for beginners, although small.