Material hack is 'allowed' on the server. Every time I've said someone is cheating it gets completely ignored. I know how to spot a cheater after 12 years of cs and I do not throw accusations lightly.. Almost 12, give or take couple of months.
I know I get a lot of those 'you're a cheating bastard', but mostly they're because I'm using a superior race or just one fitting for the current map. The only cheat I've ever used was whitewalls in 99 because my 300mhz computer couldn't really handle the game and as I was joining the military soon I couldn't upgrade ^^.
And the rest.. well I know how to listen, I'm using x-fi titanium fatality pro series with sennheiser headphones. it's not hard for me to hear which way enemies are coming from and knowing the maps and having a common sense does help.
PS. Whitewalls reduced the texturesize, so it stressed less the processor and gpu (voodoo2 ftw
sadly I had the mx version or was that the geforce).