I was upgraded to a v6 box from a TiVo and since then iPlayer is unwatchable as it buffers every few seconds and eventually freezes and the box restarts. As this is mostly what I would watch it's no use to me.
Virgin box is in the bedroom so I'm watching something to fall asleep to so I'm not watching anything particular and the noise level from adverts wakes me up again.
Other on demand channels buffer occasionally but not as badly as iPlayer. Last night it was fine for 15 mins and I thought it was sorted but then had 10 min of buffering every few seconds before I gave up again.