Yeah I've been going all out too - downloading computer game videos mostly, plus the fantastic Red vs. Blue vids made in Halo. Still got about 1GB left though.
Watchit - make sure that you reset the modem just after midnight on the evening of the 30th, then you can download for all you're worth the whole day on the 31st, and make sure you reset the modem again just before midnight on the evening of the 31st. All downloads will then be accummulated and counted as August's volume, and you'll start Septemeber with a clean slate. If you don't reset the modem just before midnight on the evening of the 31st, your download volume will be counted as part of September's allocation...