I'm the same way. Eventually, if I have played a game totally to death then I'll started adding mods, but not before. SOmebody spent time balancing the game a certain way for a reason in most cases.
Yup, that's what I actually meant. First time play-through without mods, and if I care for another play-through, I might install some user-made stuff. Frankly, the only time I did that was for System Shock 2 and Thief 2. Those were the only games I really cared to play several times, and also had some cool mods.