Yes, it's normal. They tend to use the Summer break for research, marking, admin, preparing to next semester, and the Easter one for marking, admin etc. It's not like they actually get huge amounts of time off. In fact, the hours per week they work are probably higher than many other professions. Same goes for other academic members of staff. You're just working a lot of the time! Not a 9 to 5. Oh and fewer days off than what rewt says if you are in the US. More like 20! :/