I was running Lightroom on Windows XP with 1G of memory. When I do a couple of page up or page down in the thumbnail mode (Library module, grid mode) it still takes a little while for the thumbnails to go to full resolution. I had it set to 2048 and high quality. Just a little annoying.
Supposedly you can define presets to control how Lightroom renders/converts your Raw files by adjusting the sliders including Tone, HSL, WB, Camera Calib etc etc. You can either apply the preset at import or apply it after you've imported the images. It was intimidating to see so many sliders at first, but if you've used Adobe Camera Raw to convert Raw files in Photoshop, you should be used to them. There are color differences between how my Raw files look in Nikon Capture NX and in Lightroom (default settings). Then I came across links like the following
http://seanmcfoto.com/lightroom/2007/02/lightroom-and-nikon-modes.html
by Nikonian Image Doctor Rick Walker for rendering Nikon Raw files to look like the Color Mode III in Nikon cameras. (FYI color Mode III has more saturated colors, esp greens, for outdoor shots. Color I on the other hand is meant for better skin tone renditions). And if you google "lightroom preset" you should be able to find lots of free presets that people have created. Btw, presets are nothing more than specific values for the sliders, like Red hue -25, Temp 3200K, Tint +20, Green Saturation +10, etc etc.
Looks like one should be able to adjust Lightroom to his likings, if one is more used to the look of another Raw converter.
I haven't decided if I want to buy Lightroom yet; my trial expired today. It was a good excercise to process my last shoot with it, and there are definitely things i like about it. Didn't find the Print/Slideshow/Web modules that useful though, but that's just me. I'll play with Capture ONE LE a little more.