Right now my main spends her time tanking and healing at an even 50/50 split. Healing's made me a more observant tank; I have a better appreciation of what a heal team goes through to keep my furry rump alive. Tanking hasn't exactly made me a better healer -- the two roles are so different that I even wind up redoing a portion of my UI while jumping between them -- but it's made me more forgiving of tank mistakes, and also left me in a better position to gauge whether a problem is the result of the tank or another group member. Damage-wise? Oddly enough, playing as a tank/healer for so long has made me into a hesitant DPS at best. I hate losing aggro to anyone as a tank, and hate healing oblivious DPS who pull it, and that's made me incredibly paranoid about my threat as a DPS. I watch Omen way more than I worry about my rotation.
So what role do you normally play in the game? If you change roles at all, do you notice experience from one role having an effect on how you play others?