Personally, I am not too happy with the current peak/off-peak rules.
I'd say my downloads overall are in the "low to moderate" bracket, and to me it is more important to have access to some additional quota at reasonable times, than for the off-peak quota to be particularly big. I used to use it for downloads that are out of the ordinary (like recently an SDK) or for Software Updates, or to spend some time on youTube without constantly watching my quota.
So I don't care whether the off-peak quota is 20GB or 50GB or 100GB or unlimited, but I do care about it being available to me at a time when I am likely, or can easily organise, to be at my computer. Usually that's not the case at or after 2am, and also not early enough before 8am that off-peak would be of any practical use to me. When off-peak started at midnight, I could just start Software Update then and go to sleep. As it is now, I can choose whether to take a hit on my on-peak quota or stay up into the night in order to avoid that. I have recently had to download updates for a software that I just installed, which took 600MB out of my quota, or the equivalent of two days of average use. Now there are system updates that have been waiting for two days now because of that conundrum - it would be another close to 600MB and I have not even caught up with my previous splurge. I don't like it one bit.
I'm on a naked ADSL2+ 10GB/month plan now, having over time (a bit over four years now) migrated from a 512KB/s 4GB plan at the same cost (or rather now plus the new "admin fee"). Obviously the speed is better value, as is VoIP versus Telstra, however for my usage pattern the download volume, which this discussion is about, is not. The 4GB were between 12pm and 12am, and then I had 30GB to burn between 12am and 12pm. Which I never even came close to doing, and there may have been one or two months when I came up against the 4GB limit. If we assume (for me) useful working hours from 9am to 1am, that gives me 12 hours to use my peak quota, and four hours of what for my purposes is identical with unmetered access, plus the opportunity to start larger downloads before going to bed. Now I have 10GB, full stop. Unless I want to get up in the middle of the night, which I don't particularly like doing.
My impression with all the changes up and down over the years is that Exetel tries to accommodate their high-bandwidth users whenever an opportunity arises, and then has to scale back when it finds that that clientele uses the upgraded facilities to the max. My observation is that any upgrades I have seen were always helping the leechers and not doing much for the "normal" user, and the limitations that followed impacted on both, but more the normal users. Example is the constant increase in off-peak quota (which I, for one, don't care about one bit) and the limiting of the time slot when it is offered (which I care about a lot). I think Exetel needs to ask the question which customers it wants to cater for, and define their plans accordingly.
If you offer - I don' t even know what the current limit is, 180GB? - of off-peak quota, then the leechers will set their downloaders to whatever the start time is and suck whatever you give them in the available time, saturating the available bandwidth. If that's the clientele you want to serve, then just keep doing what you're doing. If you want more "normal" and casual users who just do what they're doing and want to have some opportunity to occasionally watch some video or handle bigger downloads, that strategy won't work as well, if at all. Maybe you want to maintain separate plans for either clientele, maybe you want to have variations in your plans, or maybe you just need to make a conscious decision on who your preferred customers are and cater to them. If you haven't already done so, but my impression is that your idea of the "perfect customer" is not quite as clearly defined as it could be (apart from regularly paying their bills and stuff like that).
Personally, I'd be happy to have an off-peak quota of, say, twice to thrice the peak quota, but at times other than the middle of the night. If 12-16h is a slow time for you right now as it seems from the graph, I'd be happy to take that, too, though it would be good to have at least part of the time in the evening. Obviously a lower download allowance will average to a smaller impact on your bandwidth graph. Of course there may still be big fluctuations over the month, with some users using most of their quota as soon as they can, but it's clear that bandwidth usage is not just determined by how many users are downloading at any particular time, but also on their individual bandwidths and, effectively, quotas. I don't know how hard it would be to make either the bandwidth, or the off-peak time boundaries, or both, quota-dependent (or in other words the quota dependent on the desired bandwidth and off-peak times). Give someone more quota if they agree to be throttled to accommodate the current network load (wasn't there something like that some time ago?). Or give them more off-peak hours in exchange for a lower quota. Or any combination thereof. As I said, 10GB on peak and 20GB off-peak (or 30, like in 2006, at similar times, as in 12-12, or even 12-10) would suit my needs most of the time, and where it does not I'll be happy to accept the trade-offs (inconvenient times, lower speeds, extra payment, whatever).
It has been said that off-peak times are scheduled to coincide with times of lower load to better balance resource usage and of course that makes sense. What should also be obvious, of course, is that the whole game shifts along with any change in off-peak hours. The leechers will follow you anywhere, the normal users won't. So if you just move the general off-peak slot to 12-16h, without any other changes, you'll probably find that to be your busiest time very soon.
Anyway, just my $0.02.
P.S.: Not directly to the topic at hand, but to that of how such changes are introduced: that I was put into the situation where I had to choose between either paying $5/month more for my plan or $10 to change to the worse off-peak hours (but more quota), with the only other option being to leave Exetel for another provider (at no cost), annoyed me quite a bit. Upon my request and pointing this out, Exetel graciously waived the changing fee, but nonetheless later slapped on the $3 "admin fee", so I might well have been better off with my existing plan that was made more expensive. I feel that I am not part of the problem you are trying to address with these measures, so that adds to my perception that they hit the wrong people.
P.P.S.: And now I'm really annoyed as your forum software asked me to login again and subsequently threw away all I had written. (I already had logged in first with my forum user name and was then required to login with my customer details.) So this is an earlier copy. I can't be bothered to re-edit the whole thing, so please excuse any inconsistencies and repetitions. The final version was better but there you go.