This whole tripod/head business has the potential of being a real can of worms. I've been generally unhappy with lighter weight tripods, and have found them quite unsuitable for much of the landscape work I do here in the desert. Between high winds and the occasional earthquake, a marginal tripod does not give me the stability I need for a 10D, BG-ED3, and a longer lens (like my 100-400L).
Over the last several months, I worked my way through a succession of tripods until finally in pure desperation, I bought a Bogen 3051 to use with a 486RC2 quick-release ball head that I already owned. After playing with that combination for a while, I still wasn't totally satisfied with the stability of the setup, so I replaced the ball head with a 3047 pan/tilt head. I now have a very rigid tripod/head combination that unfortunately weighs something just slightly less than a fully loaded school bus. (nearly 20 lbs.)
Looking back, I’m more and more convinced that my biggest mistake was not my choice of tripods, but the 486RC2 ball head which seems to have more flex to it than you might expect. I suppose I’m saying that you’re mistaken if you assume the tripod legs do all the work when it comes to holding the camera motionless.
I'm back in the market for something that will be a lot more transportable, and hopefully come close to my current combination for rigidity. I’ve looked at carbon fiber units, and have not been horribly impressed with them, especially considering their price. I will buy another ball head, but it will have to be a very stout unit. It will also have to have pan capabilities.
I will be tracking this thread to see what recommendations other people come up with.