I noticed recently that Adobe added some Performance hints to their Lightroom Help. In past Lightroom posts I've gotten many comments that indicate people have problems with Lightroom performance. Here is a summary of the hint subjects, see the Adobe article for details:
My personal experience with Lightroom is that 8 GB of RAM is a better minimum than 2 GB. Ever since I configured my desktop and laptop machines with 16GB of RAM and a SSD drive ALL performance issues with Lightroom and Aperture just go away. As far as I'm concerned, I'll never own another computer that doesn't have 16GB of RAM and a SSD drive. I can't even stand to use my old MacBook Pro that just has 8GB of RAM and a mechanical hardrive.