I am suprised that so many people have no interest in african cichlids. The LFSs seem to think they are the end-all and be-all of fish with more tanks devoted to them than any other fish type (at least around here).
My weak points are just about everything. I know the basics, but the more I know, the more I realize I don't know. The scary thing is that I know a helluva lot more than just about anyone who works at any of the LFSs. My biggest weak point would be salt water, followed by african cichlids and rays.