Last week I had to stress a web portal running on x64 machine. Everything works as spected but when I tried to analyze ASP.Net counters I found there was little problem, every ASP.Net related counter was empty, I mean with no values.
And this is because my loadagent was running in 32-bit machine.
I've found http://blogs.msdn.com/edglas/archive/2006/09/06/74... but it's too late to try it :-(
This experience makes me think ... ¿Do we really need 64bit for application servers (IIS)?