In reply to markus674:
My experience: in six year's climbing fairly regularly, the biggest problem I've had is avoiding injuries. Mostly elbows and shoulders. If I had my time over I'd do the following -
1. take at least two days between sessions
2. do lots of preventative stuff from the start - ie stretching, atagonistic exercises, posture exercises
3. vary my climbing more (hold types, steepness, length etc)
4. go regularly - ie two or three times every week - rather than in patches - eg four times a week for a couple of weeks and then none