Tom,

I think it depends on what you are trying to accomplish on each platform...

Some things to look at for Unix include..

JSP - Java Server Pages
Cold Fusion ( runs on multiple platforms )
Chili soft (sp?) ( Runs ASP on a Unix box )

There is no doubt that JSP on a unix box provides somethings that certain developers do not like about a NT ASP MTS VB COM+ hell type of life ...
JSP w/unix is extremely scalable and on a more proven platform. ( hopefully this will change ) Look at companies like sprint/wal-mart/sears they are all using JSP for several reasons JSP can scale from a tiny unix box to their mainframes and they have an existing large investment in Unix and the mainframe.

my 2 cents

the law of diminishing returns applies to everything