Depends where you look, but the evidence is that it is growing as well as sections of it shrinking.
http://ubrowser.333networks.com
http://www.gametracker.com/search/ut/
http://www.serverbrowser.net/unreal-tournament

How to add more Master-servers
http://333networks.com/masterserver

[Update] The UT Community is growing! (Statistics for you)
http://www.ut99.org/viewtopic.php?f=1&amp;t=4280&amp;start=0