At about R70 per gig it is now cheaper again to rent a DVD rather than downloading one. So, to save bandwith, rent a movie today.
Other badwith saving ideas:
1) In stead of purchasing books from kalahari, loot, etc. visit your local CNA.
2) In stead of using online banking, go visit your local branch...
3) In stead of plaing online games, dust off the old monopoly, scrabble, or chess set.
4) etc.
On a slightly more serious note:
1) Get rid of spyware regurlarly
2) Use peer-to-peer only for stuff you really want. I know a lot of people who are just downloading for the sake of downloading.
3) HTTP browsing and online gaming will not easily get you to 3Gb. (=100Mb per day)