I have been on 50Mb XXL broadband for 2 months now. The service was only enabled in my area 3 months ago.
Day or night I can saturate the bandwidth. Steam downloads come down at a fast rate. 15Gb Batman Arkham City (old connection took 8 hours) in just over an hour.
If your in an area where its not had a high take up its perfect!
Gaming is perfect too, 3 of us can be playing online and it never skips a beat. Even in ping dependent Call of Duty. My ping averages 10ms :)
Best bet is to look up there community forums and see if there have been many complaints about your area before signing up.
Ive never had to call support as the connection has been faultless. However the same thing cant be said for the wireless on the superhub, but I configured my old dsl router as a access point and all sorted :) Since Ive done that I have never had to reboot the hub.
I came from BeBroadband so I didn't take this decision lightly, but there service wasn't upto what we needed.

Update 21/12/2012.
Roughly 4 months ago I upgraded early to 100mb. 100mb i do receive! :D
Day & night I can still use up every ounce of bandwidth available to me.
Top notch in SO15 area of Soton.

Update 27/02/2012
Got free upgrade to 120/12 at end of January.
http://www.speedtest.net/result/2539092949.png
As you can see I am receiving what I should be still!! :D