Users whose TV out is broken are not going to say to themselves 'Oh, maybe I should hack around with /etc/X11/xorg.conf and see if UMS option will make my TV work...'; They are just going to not use TV out.
But for us who NEED TV-out it IS an option. For me I stumble over it while debugging (all on my own, mind you, as I have filed a bugreport, but noone in the intel team seems to want to help (possibly because it is a hell to debug this kind of things without be able to have hands-on time with a failing computer)) and I *AM* very happy that UMS is an option for me.
Last week we published benchmarks looking at the ATI Radeon KMS vs. UMS performance and found the user-space mode-setting support with the ATI driver (that is also limited to using DRI1 with these older code-paths) [...]
That's exactly why there's less difference with the Intel drivers: they're still using GEM/DRI2 with UMS.