I switched from Windows to Gentoo Linux back in 2002. At this time, I tried KDE and Gnome desktop environments, picked KDE for its higher configurability and sticked with it all the time.
I love the spirit of free software and open source. Especially the following points:
If you have created something great, why not share it with others?
Work togher to achieve higher goals.
Don't work for money, work for good software!
My favorite KDE applications are KMyMoney and DigiKam.