Wow, thanks - that's another very helpful analysis of the system... I know everyone says it's simple, but I'm only just starting to 'get' it. Your advice is very sensible.
It isn't simple compared to other ISPs IMO, but the extra little bit of complexity gives us much greater flexibility than the fixed caps of other solutions and far more clarity then heavily shaped and hairy-fairy "fair use" policies found elsewhere. It doesn't work out great for everyone (particularly due to the high effective price of weekday bandwidth) but for many like myself it works out very well even after the recent changes that dropped the bandwidth value of off-peak units.
it's been educational to switch to AAISP
but then there's the school holidays which - unlike Christmas - aren't going to be unmetered, sadly...
Make it educational for the kids too: link bandwidth use to pocket money bonuses or something and teach them a little "enjoyment optimisation" that will be valuable when managing their time and resources in later life!
It doesn't take long for someone to download another 1GB
It certainly doesn't. HD content from iPlayer and the like can rack up a pile of bandwidth in very little time for instance. I'd have to implement some stringent speed limits in the weekday if I had kids anywhere near my FTTC based line: flat out at the current sync rate it can pull down 13G in an hour, a month of that would not be cheap!
Current ISP: Andrews & Arnold (AAISP, aa.net.uk) via FTTC at ~36Mbit down & ~10Mbit up, joined July 2011.
Previous setup: Be Pro with UploadPlus (ADSL2+, AnnexM), 12ish Mbit down, 1.6 up, happy customer for ~2.5 years.