Yup, it was pretty polular and recommended for a while. The chances of it working now that yields of all CPUs are up is minimal, as the X3's with an extra core were basically X4's that had either a faulty core or were bumped down to X3 to meet demand. Chances of a successful unlock are slim, but there's no harm in trying it.
I've recently unlocked a Phenom II x2 545 dual core to a Phenom II x4 Quad core and it's stable so it is definitely possible. Just bare in mind the newer the chip the slimmer the chance as JackSprat says.
Keep an eye on voltages and temps as sometimes the extra cores need a little more juice than the certified AMD quad cores. CPU-Z will help you with that.
I was expecting it to take me to the bios or some other dark place but instead it just turned itself off and rebooted. Then when I got to the desktop a notification popped up to say new drivers successfully installed please restart for changes to take effect. So I restarted. Now where it used to say press 4 for Asus core unlocker it now says '4 cores are activated!!' So then I went straight to control panel/system info and it says the following:
Coretemp is good for monitoring temps. To make sure the system is stable I would recommend running a stress test for at least a few hours. Something like the latest prime95 will do nicely. Pay close attention to the temps here for at least the first 15mins, if it goes any higher than 70-75c I would stop the stress test and undo the core unlock.
Thanks GuitarJim. I've done what you said and just run Prime95 (I selected the first box small FFTs, not sure why) CoreTemp gives me one reading rather than for each core. It started off at 37c and gradually began to rise as soon as I started the test. Within a couple of minutes it got to 74c so I stopped it... Then I came here to tell you about it.
I tried it again and this time and kept it on the 'blend' option which is the setting the program defaults to when you open it. I ran for half an hour this time, CoreTemp shows 100% load on each core as it did before. The first 15 minutes temperature was 73-75c the last 15 minutes was about 75-77c. It didn't go any higher than 77 but probably could have done if I left it longer. So what should I do now? Buy a new fan?
It's probably a good idea to get a new fan, the Coolermaster Hyper 212 plus would be a good idea if it will fit in your case. You could also try fiddling with the core voltage if you feel confident enough. What is your max voltage read out in CPU-Z? It shouldn't really be going over 1.5v with a preferably of 1.425v or less.