The biggest problem I have with forensic shows (and I'm a huge fan!) is the time frame.

They get DNA in hours, Trace has all fibers and particulates off the body in minutes, computers run through ALL KNOWN DATABASES within seconds, and the reality is that a lot of time-consuming hard work by no-name lab rats is left out because it doesn't make for good television.

You'll note that is my biggest problem.
Not my only one. :)