I've had one for about 4 months now...2003 DH50. I put the DNM shock on the front that is supposed to be crap.
Bombing downhill is easy, taking big drops is easy, dirt jumping is easy, urban is easy, skate park riding is easy.....that said, riding uphill is a pain in the ass.
The 2003 actually comes with 7" travel (upgrade from the 2002 version) and a romic rear shock. The shock, when setup for your weight works like a champ. The frame is tall and I ride a medium instead of a large even though KHS recommended large. If you are petite (5' 5' and under) you may want to try the small frame if you can find it. Riding is the best way to judge.
The weight is comparable to any other DH bike...yes it's heavy. My complete bike is about 45lbs. That said, it feels sturdy on drops etc. As for the rear flexing, I like the feel of it so it's no big deal. The bike doesn't flex any more than a single pivot bike. Most of the flex is probably because of the QR rear wheel.
The DNM fork has done me well so far and feels very solid. You'll find some people say that they are hard to adjust; this is true. The rebound damper has about a 1/8" turn from totally on to totally off. That said, once you have it just right, the fork works like a champ.
Finally, I have had two bikes replaced and a lot of support from KHS in the past. Red5 had a bad experience and that totally sucks, but I can't say I have had less than full cooperation over the last 3-4 years.
PM me if you want to see pics etc...and good luck.