Executive summary:
Linux is not for the faint of heart. Educated, motivated users only. Free, configurable, time intensive at first.
Windows: easier, but limited ability to explore environment. Bring lots of money to by the OS, applications. Most users are familiar with this.
As mentioned on
http://ask.slashdot.org/comments.pl?sid=44997&cid=4681965
the goals of the two OS are different. What are your priorities for computing?
Bias disclosure: after running Windows XP since 2001 (Mac before that), I switched to Ubuntu 8.10 Intrepid Ibex in December 2008.
Below is a comparison of WinXP Pro SP2 versus Ubuntu 8.10 as of Jan 2009
Cross-platform programs, free
wireshark [packet sniffing]
firefox [web browser]