Ingo's performance counter infrastructure is a bit pointless. All it does is distract from the actual performance counter implementations that are trying to be merged (admittedly those partially sat outside of the kernel a bit too long).
If Ingo ever addresses the shortcomings brought up on the linux-kernel list (he hasn't) or ever tries to implement things on a machine that isn't a Core 2 Duo machine (most notably, Pentium 4 or PowerPC) he'll find out that things get complicated quickly. And the kernel is not the place for these complications.
It's a big mess, and a big frustration to those of us who use performance counters regularly and have to look forward to the prospect of patching our kernels by hand for years to come because an inferior infrastructure useful more-or-less only to Ingo gets merged.