I've been using Photoshop Elements for a few years now, and it was okay, but I upgraded my camera a year ago and started using Adobe Lightroom (another product that rocks my boat!), and I wanted to use a product that was well-integrated with Lightroom; Elements just wasn't there. Enter CS5.
I forgot to mention, too, that I recently made the switch to a Mac at home, so I needed to buy new licenses for everything anyhow. Not only was I looking for a photo editor and a DAM (digital asset manager) tool, I needed a panorama stitcher and an HDR tool. Lightroom is taking care of DAM, and CS5 is taking care of the rest.