Hi Jez:
The ride is really smooth and to be honest the only time I've seen the forks visibly flex has been under braking in the gloop and rain recently, in the dry the braking is excellent and the fork behaves itself.
To explain, I'm using Avid Ultimates with ceramic rims and the rims are starting to show a little pitting here and there, I think that and the fact that the pads (for ceramic rims BTW) had worn and needed re-aligning is what made the braking a touch 'grabby'. They have been fine since then. I don't know if a P2 steel fork would have flexed much less under the same conditions.
I'm sure I read on one of the US sites (it could have been MTBR) that XACD had addressed and rectified this problem with their forks, also it was intimated that the people that had broken the forks had been doing drops, jumps etc when this particular fork should only be used for XC.
HTH