I have the same problem. Paying nearly £90.00/month for up to 70Mb/s, last night downloadspeed was 0.74 Mb/s. Systems such as BBC iplayer and even TV Anywhere were unusable due to buffering every second.
Reported problem and was told it was down to people using the system! I don't know what else Virginmedia expected its customers to do! They still expect their money every month though.
Tested gain this morning - an improvment - speed now up to 1.2 Mb/s. Wonderful. I am suprised that Sir Richard Branson is allowing Virginmedia to damage his brand name.