I do all my work in CS5, mostly in ACR (Adobe Camera Raw). ACR can do maybe 90% of the adjustments that a photographer needs, then I finish off in CS5. I can recommend the Scott Kelby book 'CS5 for digital photographers' and also his websites
http://kelbytv.com/ http://www.scottkelby.com/blog/ http://www.photoshopuser.com/ and the video podcasts
http://kelbytv.com/photoshopkillertips/ http://kelbytv.com/photoshopusertv/