Same here. Vista here as well. (Final, not beta) Paint.net is chewing away at @30% cpu with a selection. But, I noticed that this causes the vista window manager (dwm.exe) to crank at about 30% along with Paint.net. Now I see/feel that while using the desktop. Putting total CPU at about 60% use just when a selection is made. Toggling between apps to test images in web pages and such, you really feel it as browser reloads, switching windows, etc lag a little more. No other apps that I've tried seems to cause this. I use paint.net for so much of my graphics editing, I haven't even installed Photoshop CS yet on my new vista install. I suppose I *could* install it and test to see if it's selection does the same... but don't need the bloat or loss of HD space if I don't need to (lappy).