I'm with Virgin (ex-NTL as well) and it works perfectly. I can't remember the last time it DC'd me from WoW, usually it is the game crashing if I go online suddenly. There is some occasional downtime, maybe a few days per year, but I've not seen any ISP that doesn't have that.
We had one problem about 3 years ago where it reset every 10-15 mins, but turned out to be a faulty component in the wall box outside. They replaced it in a few days, although convincing them it needed looking at took a lot longer (not in my name so I couldn't talk to them). The key is to get past the call centre onto someone who isn't reading from a script but again most companies are the same nowdays.
I've had bad experiences with BT accounts though. I had a 12 month contract but we moved out of our flat after 3 months. I phoned up to say we had gone, but I would carry on paying each month until it was up to honour the contract as I couldn't afford to pay it all in one go. They said that would be fine then took 9 months payment plus a fee the next day putting me over my overdraft limit and costing me almost £150 extra in bank fines on top. Not surprisingly I'm not planning on ever using them again

. I also do whatever I can to not use Direct Debit after that, they can take any amount without letting you know as you sign away your right to prior notification of changes.