most of the fluid range is well suited to what their intended for, but i agree the mayhem/tantrum are a bit of a letdown, basicly they started with an alright frame and wheelset then munted it, cranks have major issues (not so much the newer ones) its still running a tripple ring setup which for a DJ bike is useless, and they use el'cheapo rear derailers, which, because of the massive amount of chain needed for the tripple ring setup to work, are long cage, and we all know long cage derailers are more prone to everything breaking.
if i owned one i would replace the tripple ring for a dual ring with bash or a chain device, then replace the derailer with a 105 roadie derailer. half decent set of cranks... maybe SLX or the older octalinks would still handle most stuff. and then it'ld be a fairly decent bike. you can't realy expect much better from the fork at this price point, the only forks i've seen break are from cases/abuse and even high quality forks can do that.
still if your after a dedicated DJ bike, a BMX will get you much more reliability for your buck than ANY MTB.