It's been great for me, have at least $200 worth of games that were free via PS plus. You have to think of it more like renting games for an indefinite period, similar to how services like quickflix and such work. inFamous 2 for example is a good one for me, great game, didn't finish it when I rented it but wouldn't buy it as I know I'd only play through it once and never touch it again. This way I can finish it when it's convenient, delete it and grab something else they're offering. It's also a great way to try out games you may not otherwise try without having to worry about regretting a purchase.
The automatic updates only download patches for recently played games, forget whether it's the last 10 or 20 you played but it's certainly not all of them. You can disable them altogether anyway. Most countries don't have a cap so they didn't really design it with Aussies in mind, but I have a 500GB quota I've never managed to use up anyway so it's never worried me. It's great when there's a huge update, like one I had a whole ago that was 1.5GB, much better just launching the game and it installing instead of having to wait an hour for it to download first.
It's real value comes from the discounts though, saved at least $50 in the last 6 months from the discounts. So it's definitely best value to folks who buy PSN titles or DLC regularly.
~ PSN - Trent_Steele ~ Steam
~ Battle.net - Chief#6843