Facemelt Loon

I've been running Second Life viewer 2 on an iMac 2.66 Ghz Intel with 4GB Ram and an ATI Radeon 4850 which is in full compliance with second life's recommended specifications. It has been running fine up until last night, when I run Viewer 2, it alerts me that my system doesn't meet minimum specifications, and sl runs like poop. It won't load anything. It even takes time to load the preferences pane before even logging in, so it feels as though it's running on a very old machine, but all other software is running fine, even programs that require a lot more from my system. I've just downloaded it in WIndows 7 on Parallels, and it's running a little better, but still slower than usual. Has anyone ever heard of this before? Has your system suddenly forgotten how to run Second Life Viewer 2? If so, did you find a way to remedy it?