We had quite the mix of bikes amongst us, from CF hardtail flatbar (with accompanying exploding XTR RD
) to my Yeti 575 - that's if you exclude the DH rigs that a couple of the guys used almost exclusively on the specific DH trails. I say almost, because they ran the DH rigs down the Delatite Trail on our last run on the first day. Needless to say, they blasted off into a cloud of dust as soon as the trail pointed down (which was most of the time), but were off the rigs and walking as soon as the trail pointed up hill. The point being, you can get about on pretty much anything if you ride to the bikes ability and the trail conditions. Of course, if you're Suffer on a mid 90's Trek Y frame with rim braks, flats and questionable suspension, then you throw that theory out the window..
On a personal level, I have found the 575 to be more bike than necessary for the trails that I ride mostly (Lysterfield) and I tend to run the Talas forks at their mid setting (120mm) for most of the time. However, places like Buller really see the 575 and it's ilk come into their own with the broad mix of climbing, descending and technical trails that you come across. It also gave me a new found appreciation of the flexibility that an adjustable height fork like the Talas provide. Climbing some of the steep, tight switchbacks that we found on trails like Misty Twist was far easier once I remembered to drop the forks down to 100mm (and this is where we saw some of the 29'er guys struggle). Then cranking them up to 140mm for some of the technical and high speed descents like Copperhead and Delatite meant I didn't end up with any of the upper body soreness that the others mentioned.
Of course I could adopt Snuffy's approach....but then I'd have been riding Buller on my old Redline Proline BMX race machine - single speed & fully rigid! But I say if the technology is there, use it