I put up with the worst of it for about six weeks and then I cancelled. I have no way of knowing for sure, but I guessed that their algorithm was based upon how quickly they received things back, not overall time or throughput. If I returned too quickly, they would just slow down the whole process. I would get aggravated and try to return my DVD quicker hoping to speed things up and it had the opposite effect.
The final straw was when I received a DVD that was broken. It had a crack completely through it so that it looked like a big split washer. I noted it as broken from my account and returned it. I re-requested the same title and they sent me the same damn broken DVD. I threw my hands up and said enough. Two weeks wasted on the same title and I still haven't seen it.
I will note that this was around 2004 or 2005. I have no idea if they still throttle. The Post Office recently closed our local distribution center and moved it all to the other side of the state. Mail takes an additional day now, each direction. I would guess that DVDs by mail would be 7 day turnarounds minimum these days.
From a business standpoint, I understand Netflix's reasons. Give the best service to new customers and least cost customers. Screw the expensive customers because they aren't profitable.