A wide variety of things.
One of my buddies had a new one (I think a Tactical II) that the slide was not cut correctly so you actually could not pull the slide back when it was locked back empty. You had to use the slide release, pulling it back to charge it after locking back would not work.
I've heard of several online postings about Failure to Feed problems, and a good deal of fit/finish complaints.
All of which were fixed by Kimber at no charge, but they are not necessarily an out of the box stack your life on it gun