Hoi Rudi,
CentOS is great as a server OS, but it won't replace our accountant's Windows 7 desktop - the amount of technical compatibilies issues we're going to sit with is just not worth it.
Don't use a jack hammer to drive in a nail :)
Centos 5.5 works well for my non-computer literate friends who use a computer for Facebook and web browsing.
I use Centos 5.6 on servers, desktops, home server/desktop, laptop, notebook/netbook and would never willingly return to ghastly M$ Windoze.