No more or less than on a geared bike. A 9spd rear wheel is somewhat less strong than a singlespeed-specific one, but if you don't tend to bust 9spd wheels it won't be a problem.
I have also thought about the gears again Dylan - but everytime I think hard about it I realise that I really do like the simplicity of the one gear system - probably will put the gears back on soon though, or maybe move to a 14T or 15T cog on the back - for the faster courses!!!!
I ran 32:16 at SITS last year and it was about right. I dunno how strong you are, but over 24 hours it worked for me. You're never going to take on geared bikes on the downhills anyway, so you want something your can turn over on the climbs and gives you enough kick in the singletrack. If you're going to swap cogs, remember you'll need a longer / shorter chain depending on which way you go.
I tend to run a big, wide riser on my Voodoo for more leverage on the climbs. I don't see why you shouldn't use carbon, but you'll probably feel a bit of flex when you're out of the saddle and really pulling on the bars. I just use uncut Easton EA70 riser bars cos they're nice and wide.
Wheels? Like Mike D says, no more so that on geared bikes. I've been running Bontrager Race X LIte Discs on mine which are very lightweight 28-spokers and haven't had any problems bar trashing the bearings once.