I've been using ntune 6 beta, I really don't recommend you let it find the "optimum" speeds for your graphics card. It picks something different every time for mine, and I mean drastically different, whatever it picks is way above what I'd normally risk and usually ends with the system locking up.

The new monitor is pretty cool, if you're into graphically appealing things. It's a sreen showing the components in your PC (CPU, GPU, Memory, etc) and when you click them, they rotate around and give you some more info like temperatures, usage etc. Doesn't seem to impact performance but it does cover the screen and you can't do anything with it showing, I've been told in Vista it can be set as a desktop which would be more useful.
It's nice to see shader overclocking in there though, works pretty well. I think it needs a lot of work as is, but it's only a beta so it'll probably be improved. ntune 5 was pretty good though, if you don't want to bother with hundreds of different tools. The stability tester isn't too good in my opinion, but I've found the best stability test is to actually play games that are sensitive to overclocks like Oblivion. If you have a second monitor, it's useful to have the temperature monitor running on that while you're playing a game.
I don't know if it's just me, but I get this weird problem where the control panel randomly refreshes itself a few times. It's the same on both of my machines and I've tried on the machines at university and they're the same too. Is it something I'm doing wrong?