I'm on a Talk Talk Unlimited package, and I've not had any problems with it. I'm aware that they do traffic shaping on Peer to Peer sharing at peak times, but as I don't use those, I've never noticed it - doesn't seem to affect anything else, eg iPlayer. It's all been pretty good for me, and despite some heavy usage some months, I've not had any contact saying I was using it unreasonably.
So for me, it's been unlimited.
They're currently doing an offer with a free YouView Freeview/IPStreaming TV box thing (though there's a £50 install charge). Am tempted myself.
Ian