A quick calculation from January's stats.
looks like at about 900 'hits' per day to cow (this is taking all 5 frames and treating as one) it works out to about 10k of data (html mostly) being send from cow.pl per 'hit/command/refresh'
Keeing in mind a quick refresh will be less than 1k (most of the time) and examining the manual or an image will be a fair bit more.
For January this was 350Mb in total.. for 3-4 users :-)