Monitoring bandwidth usage!
ISPs around the world are more and more implementing bandwidth caps. We've had these caps in Canada for years, but bandwidth monitoring is even more important now that most ISPs are going in that direction (Comcast with the 250 GB limit). I still haven't found anything that really works well for monitoring usage directly on the router, but there are quick and easy options for monitoring it on your Mac. Of course, there are numerous disadvantages: all bandwidth going through Airport is counted, including file transfers between Macs and you have to monitor it on each computer separately. The one that I use is not ideal because it resets every time you restart your Mac. There are probably better applications that don't do this, but this one just appeals to me because I use it anyway for many other things. It is iStatMenu. If you add the Network menu to your menu bar, iStatMenu will keep track of bandwidth used and you can access it at anytime in the menu. It works pretty well for me because I don't use Airport for file transfers (Ethernet is fast for that!) and I nearly never restart. The same application also provides Uptime in the CPU menu so you can get an idea of the period of time that bandwidth was used. More info and download link here on MacUpdate.