Slowjo: excellent points but most folk don't wanna hear that – they wanna know how much better a rider they'll be if they spend more money.
My LBS guy (who's an ex pro MTB racer) reckons that Deore Cranksets are the best coz they're the only ones that "never bend".
Personally I'll stick on whatever's best value – and at £55 with BB Deore is hard to beat. Besides, it doesn't matter how nice and shiny parts look because after a few decent rides they'll look like sh*t anyway.