I just found this on the web today: http://www.eweek.com/article2/0,1759,1645550,00.asp
Apparently .NET did pretty well against WebSphere.
Disclaimer: Now, I'm as skeptical as the next guy when it comes to studies, but and I have virtually no knowlege of WebSphere, so I can't validate nor discount the study.
Anyway, I just thought it was interesting. You can draw your own conclusions.
As for me, I'll be working hard on the Whidbey NGEN tool to enhance the performance of your future .NET applications.