Your sig is apropos for me today. I did an upgrade of Fedora 8 to Fedora 9 today (on my workstation, not a server of course) and killed X. Fixed it though.
The CentOS people do a lot of testing and their wiki articles are also reviewed--so, in general (I'm sure there are exceptions), if the wiki says it is safe, it probably is.
Of course, stukov does have that test box, in case it isn't.