I recently upgraded to CS4 and acquired Lightroom for the first time.
CS4's 'Camera RAW' has really simplyfied my post. Firstly, you can correct jpgs and tiff files in Camera RAW as well as RAW - I shoot RAW.
Having tweaked the image in Camera RAW, I open it in CS4 and look at the crop, backscatter, sharpening and noise. Plugs-ins really help here.
Try Nik Software Dfine (noise), Silver Efex (B&W conversion) and Sharpener Pro (sharpening). I also use Focus Magic as its quite good for correcting motion blur.
I'm still getting my head around Lightroom but it seems to offer a more intuitive interface than CS4 but also reduced capability. Its archiving tool looks to be very powerful. It runs happily on my 10" netbook (which CS4 does not) so will make good travelling software when I have absorbed Scott Kelby's tome on the subject. BTW. His Photoshop tutorial books are highly recommended.
HTH, Tim
Avoid me, you know it makes sense...