This is making the rounds internally and worth posting here.  Not brand new - but just due to the sheer exhaustive volume of guidance in this - if you haven't seen it yet it's worth reading and keeping around as a reference:

"Improving .NET Application Performance and Scalability"
http://msdn.microsoft.com/library/default.asp?url=/library/en-us/dnpag/html/scalenet.asp

It's a free PDF download - but realize that it's 1120 printed pages before you go to print.  :) 

[ejarvi]