I strongly dislike a tablet for programming. I even have a tablet laptop I "permanently borrowed" from my girlfriend, and even the idea of using that for any aspect of programming just makes me cringe.
My left hand is always on the keyboard, while my right is jumping to and from the mouse. Because the left is on the keyboard all the time, it is also the most logical hand to perform shortcuts with. Tablets lack the convenience of "quick-switches" due to the pen. Even if you did not have to use the pen, it is unlikely you will be able to achieve the same kind of speed of switching to your tablet, moving slightly, then switching back, as you can with a mouse.
Finally, even if you are as quick with a tablet as you are with a mouse, buttons are in a much less convenient location. Who looks at their mouse when clicking a button? I'd hope nobody. Now, who looks at their tablet? Hmm, I see a lot more hands in the air.
If a tablet suits you, then sure, go for it. But you have to be pretty bad with a mouse to be better with a tablet.
If the reason you want to switch or have switched is due to comfort, either get a new mouse, one of those (often gel-like) wrist rests, or physically reposition yourself. There is a solution to the discomfort, and it's not in the form of a tablet.