I'm getting ready to start my 2nd year at UCSF in about a month. If you were a science major (I was), it's not that bad. I graduated in 1997, took classes in Fall 1999 - Spring 2000 and started med school in the Fall of 2001. If you're weaker in some sciences, it may be a little tougher and/or you may have to learn more background info on your own. That's what happened to a lot of the non-science majors in my class - they got cuaght up on the cell bio knowledge they were presumed to already have.
But, otherwise, pretty much everything you need to know is given to you - it's all a matter of time management and getting used to not having nights and weekends free at first. You will, with time, get used to what is expected of you and how far you can push the timing with respect to studying, etc. I started out studying a lot more at the beginning of the year until I figured out what I could get by on and what was really important to study (for exams). Then, you slowly learn how to get free time back and how to have as much fun as possible when there's not an exam.
Granted, I am talking from a pass/fail perspective and a new curriculum. But, I think it's not that bad to have a break - it made me more excited to learn and helped me not burn out from the volume of material presented to us. Good luck!!