I bought the Manfrotto 680B 4 years ago and it worked fine at the time. I haven't used it in over a year or so. I've been hand holding an Alien Bees ABR800 ring flash with a 70-200, sometimes tripod'ing it. Then I remembered I had the monopod and tried my setup on it and the monopod doesn't really support it (segments start to compress if you put any extra pressure downwards). The 5D Mark II + BG-E6 + 70-200 + ABR800 is under 11lbs (weighed it on a shipping scale), and the 680B is spec'ed to handle 22lbs. Apparently that's not the case.
Anyway, I'm looking for a monopod with more strength, or perhaps one that actually handles the load it's rated for.