I am tired of hearing people recommend that you should use only one thread per process, while many programs use up to 100 per process! take for example some common programs

vb.net ide uses about 25 thread when not debugging
System uses about 100
chrome uses about 19
Avira uses more than about 50

Any time I post a thread related question, I am reminded almost every time that I should not use more that one thread per process, and all the programs I mention above are ruining on my system with a single processor.

What constitutes proper use of threads in programming?

Please make general comment, but I'd prefer .NET framework

thanks

EDIT

changed processor to process