We had so many problems with it that we went over to Sky. They were forever crashing and we could never get through on the phone. Bad service. Slow speeds, never seemed to get what we were paying for. That was about 3 years ago though so may have changed now.
A friend and my sister are both using PlusNet, and I'd sure as heck know if they were having problems.
The best suggestion I can make is to have a look at ThinkBroadband and compare them with some of the other ISPs you have heard of.
They were criticised for having an 18 month minimum contract and have reduced that, but you also need to consider how much data your household uses (send and receive) and whether their traffic management will get in the way.
On the ThinkBroadband forum someone asked about PlusNet vs TalkTalk and one of the site owners (who gets interviewed on radio and in print) said that both manage traffic (slow down file sharing, to let people browse faster, all day and up to midnight) but PlusNet is more 'open' about it. Also worth checking alternative ISPs forum areas to see what grumbles there are about speeds etc.
Sorry to read of another having problems - when I was using them (I moved and have no landline at present) they were pretty good and were open 24x7 They have picked up awards for being a good ISP for home users.