We have 3 other new computers in our office that we are installing with XP Pro. My computer is the only one that will remain and it has 2K Pro. I have XP at home on one of our computers and we like it better than 2K Pro, especially now that SP2 is out with the added Internet features and security features. I'm still using Adsubtract for my pop-up blocker and it's a pain when I want to see a pop-up on a site. XP pop-up blocker is far superior IMO and experience thus far. I took my wife's XP computer away from her to give to our daughter and she got another 2K Pro computer we had... now she wants XP back and our daughter doesn't want to give it up. The wife's computer is a better built system so I'll let the daughter keep hers and upgrade the wife's. There are various other reasons and also things we like about XP as well... I won't go into all of them.
As far as upgrading is concerned... I want to save my Microsoft Office Small Business, our finance and accounting software for our office (which is a bull to reload) and I have several other applications that I'd just rather keep on the computer and not have to reload them... just makes life easier.
I have just learned from our local PC store that I can upgrade using the Full Version as they have done it on several occasions for other clients. He made me a rather good deal on a pair... one for my office computer and one for that last home computer still on 2K Pro.