I was a TA during my first year of grad school before settling on a research group and taking an RA. After a year with my research advisor, I was asked to TA the course he taught so I had a TA and an RA at the same time.
It was one of those 350 student courses at a large university, so we also had undergrad "graders" who'd grade the homework assignments... I wrote the solutions to the homework, kept the gradebook, manned the message boards, and held office hours.
Teaching can be a lot of fun and very rewarding, but most of the time it sucks and I yelled at people a lot. I was notorious for yelling at people for not knowing how to do math, not reading the book, not thinking, etc.
I was also voted TA of the year for the department.