Sorry for the late reply here. December was a busy month for me at work. It cut down on my surfing time somewhat.
Like Greg K, I used the free trial for a month on my laptop running Windows Vista. I love it, and I haven't had any issues with the program so far. I must admit though, running with Vista I was holding my breath, but alas, no problems thankfully. I went ahead and just purchased the full version.
Getting rid of GRLevel3 toolbars & sidebars make a HUGE difference when running GRLevel3 in four window pane mode on my laptop. I'm going to try to convince my brother to buy a copy for his computer and take a look at GRLevel3 on his 27 inch monitor. I'm drooling just thinking about that. lol