Generally the only thing that is heavily throttled these days is P2P traffic - IIRC if your a heavy user (over 300gig) then SSL connections, etc. will also be throttled to 2Mbit/s during peak times.
BT have changed the whole traffic management system now so it works by a "soft braking" principle taking overall traffic levels into account and then when the network starts to get busy it will start to slow down heavier users a little bit - in most cases you probably won't even notice it.
Using 2-3TB a month is gonna put you at the front of the line for traffic management tho and you'll feel it more at peak times than someone who DLs say 100gig - purely just as an example you might be slowed down to the point where your limited to 5MBit/s throughput whereas at the same time someone who has DLD 300gig is limited to 7Mbit/s.
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Edited by Rroff (Fri 30-Dec-11 21:06:00)