If you are an Internode user, and your wanting to keep tabs on your data usage, there is this small utility available from Internode at … http://www.users.on.net/~spohlenz/internode/
There is one small issue though, if you were using Ubuntu Intrepid and upgraded to Jaunty, the version of python that you used to install it originally has changed! so once in Jaunty your left with a broken usage meter! Alas… all is not lost, to get it working again you'll have to download the source from the link above, extract it then simply re-install by "sudo python setup.py install" (you had already done this when you first installed it!)
So now you have a functional usage meter again!
Proving that the functionality really works!