I actually have had trouble. I went to Cancun August of '10 and it wasn't a big deal (older manfrotto with showing spikes without any rubber feet and all alum) but when I left Cancun and flew to LA (a stop over in texas first) the TSA fella at the gate was about to take the tripod away from me.
He mentioned it could have been a club like object but I explained (in a very calm manner) that it was just a tripod and I have had no trouble with any other airport that I was at, the 5-6 times I went through security. I was also traveling in a suit, he mentioned since I'm such a polite young man and that I meant no harm that I could continue on without him jacking my $100 pos tripod.
I'm not really sure where he got polite though.