Been with plusnet around 6 months now and have had a stable connection on ADSL.
Speed is around 15mb.
I've only had one issue with plusnet since I've been with them and it was when I moved home. I moved on the same exchange so I got to keep my phone number which was good. I moved closer to the exchange but for some reason after the move my upstream sync got capped at 448kbps.
A quick phone call to support and a few days later this was returned to around 1mbps upload.
Also I no longer use their ADSL router the wireless wasn't great and I like to use gigabit for wired connections.
Using a modem and a netgear router with PPPoE and it works great.