Plusnet were a great ISP, don't get me wrong. Now I think they are becoming a loss leader. Reason being is they used to have a reasonable pricing structure and didn't advertise much (a quiet, niche ISP), but nowadays I feel they are selling it off cheap and spreading it to the masses.
When I was with Plusnet (it was ADSL Max I should say), my download speed dropped from 6.5 Meg down to 3 Meg during peak times.
Some activities - namely YouTube streaming, gaming and downloading from Steam seemed to be slow all day (even when my connection speed was 6.5 Meg) this indicates rather heavy throttling in certain areas. Yes, peer-to-peer is throttled (or as they put it,
slowed down).
Other things to consider are that I think the support is going downhill. It appears there are a few threads on here of late where support have made significant mistakes (lost them now but I'm sure I've seen some).
Something they did to me was when I called to complain about my performance due to throttling, the guy on the end of the phone was looking at my IP profile (set speed) and he set it to 0.5 by mistake. As I noticed the large drop in speed, I reported it as a fault. I suffered 1 week of a download speed of 0.29 Meg during which all Plusnet did was send me pretty speed graphs. They didn't tell me what the issue was in the end, the profile just sorted itself out and the stagnant support ticket was closed over time. I only realized what they'd done once I had put 2 and 2 together.
I'm with Sky now and it performs top notch, I haven't needed to contact support and the price is very good.