I've got a Linksys WRT-something-or-other router which I've installed DD-WRT on. Recent versions of the firmware have a section that keeps track of overall traffic through WAN that your router handles. It also makes it pretty easy to do a little calculation of your own with it since you can download the data in text format. It logs in terms of total data in and out per day of each month. November was my first full month of data excluding the the first of the month (something broke that day I guess), so I downloaded the log and looked at November's data.

On average we downloaded 1917MB per day and uploaded 562MB per day. This is the total traffic between 3 people. Grand total we downloaded 54GB and uploaded 16GB. If we take a look at the ratio between the two I can approximate what our actual bandwidth is. We're supposed to have a 20Mb down connection and the ratio suggests that our up bandwidth is ~5.86Mb which means our maximum upload rate is 750KB/s which we've never achieved before. When I use bittorrent to download Linux ISO's I assume that in order to not choke our router with ACK's I need to throttle the upload rate to about 70% of the maximum which hovers around about 120-130KB/s which is ~1Mb/s even and that's only 70% of the max.

Basically I wouldn't survive if I had Comcast and a 250GB limit per year.