I have Sky Broadband and at first it was terrible, but now seems to work more often than it doesn't. It still isn't perfect but at least it's usable.
Ordering it was a bit of a pain, firstly they got the MAC code wrong that we gave them from BT and we had to get a new one from BT so that they could try again and this time it worked. Then they activated the line to Sky from BT on time - however the Sky router was nowhere in sight. Couldn't use the old BT one to connect either because they hardcode the username and password for the connection into the router so I didn't have a username and password to put into my BT router to connect for the time being so was stuck on dial up for about a week until they sent a second router that eventually turned up.
However all now seems to be working OK, you just get the odd disconection and sometimes it loses it's DNS servers which can be annoying, but this isn't a frequent as it used to be.