I suppose I'll add my own two-cents to this conversation. I also have a Wacom tablet, and while it doesn't work well inside Trainz, I use it for almost everything else. Pretty much the only time I use a mouse these days is when I'm inside Trainz or some fullscreen game. I love the absolute positioning of the pen -- once you get used to the mapping between the tablet and screen, you can pop all over the screen so quickly. And it's been nicer to my wrist than a mouse was.
Anyway, obviously people have a lot of varied opinions about using a tablet, that's just my preference. Like the others in this thread said, it doesn't work too well inside Trainz. The Trainz user-interface really assumes you have a scroll-wheel, and the right-click sensitivities are designed around the kinds of movements a person normally does with a mouse. So if you only wanted the tablet for route creation, don't buy one. I love tablets for other purposes though.
- Madeline