Since my ISP has recently imposed a 3gb/m limit on my ADSL (with loosely
defined 'free' sites) I was considering making a setup to use ipf and
rrdtool to keep tabs on my hourly/daily usage.

Before setting out into the unknown (I'm a beginner really) I was wondering
if anyone has done this already.

I'm using simple rules such as:
count in on ppp0 from any to any
count out on ppp0 from any to any

and also some extended rules:
count in on le0 from 10.0.0.1 to !10.0.0.10
count out on le0 from !10.0.0.10 to 10.0.0.1

for each pc to show the amount of real traffic being sent through ipnat.

ipacct is good, but not right for what I need, so if anyone has an rrdtool
based setup going already, feel free to let me know :)

TIA,
Gwilym