How long has it been since you last DU'd? What packages are you holding back? What versions do you have installed? Also important: What is your hardware like? what video drivers are you using?
There have been a number of times in sid's history when there were version conflicts, errors, etc.
Point in case: I don't think we can give you any solid "reputable" advice without more info. If you want to know about recent issues with upgrading, you could have glanced at the front page of upgrade warnings and clicked on the top few posts to get a decent idea of what these issues are, which are fixed, etc.
I hope I helped.