As someone who recently had their VIP expire and is working to get it back, it can be a frustrating system, but I admire the idea behind it. It's a way to encourage active forum members and the minimum character limit encourages more meaningful discussion.
The 7 posts per day average is interesting, though, as it does put things a bit in perspective. Miss a couple days and suddenly you're looking at 21 posts in a day to make it up. Miss a week for a vacation or something (not that I remember what a vacation is) and you're posting almost 50 times in one day to stay on target.
I think the system works, but I do wonder if the threshold is in the right place. I think 3-5 posts per day is a reasonable level of activity, personally, but I'm not sure how the system would change if the VIP cost were lowered to $YTT100 or so.