As many ISP now have data limits (quotas), be it hard or soft. With Hard limits they cut you off once over your quota or switch over to billing you a lot per MB, with a soft limit they just slow down your access.
Virgin.net will take your bandwidth down to 50% or 25% of the amount you pay for depending on tarrif. This is triggered by down loading 500MB (depends on tariff) between the hours of 4pm and 9pm. once triggered the reduced BW will stay in place for 5 hours.
Also note that the 500MB is less than half a movie rented from itunes, which means that are destroying the apple movie rental business!
For an 8Mb (Mega-bit) broadband full speed is actually 640KB /s (Kilo-Bytes)
500MB / 0.64 = 781.25 Seconds =13Minutes
The reduced BW can be triggered in just over 13 Minutes!
My experience for there non-cable 8MB connection reduced BW is 10KB/s Which is way beyond what they claim to reduce your BW to.
because of this it is useful to keep track of the BW that you home network is using. this is easy to do (I guess) if you only have one computer but if you have multiple machines or live in a flat with flatmates then the BW measuring must be done at a central point. For me my mini-itx server uses about 90% of my bandwidth so just measuring this should be good enough.
For Ubuntu (from a terminal do)
$sudo apt-get update
$apt-cache search ethstatus
$sudo apt-get install ethstatus
launch with in a terminal by calling
Just need to work out how to make it clear/keep daily/monthly totals.
NB : Added 01/12/2008
Just found the ADSL Managment page for my isp