For me, the most important thing is the new raw processing in Lightroom 1.1 or Camera Raw 4.1 (available only for PS CS3; won't work with CS2).
LR isn't a good choice for fine-art prints because (1) it has no soft proofing, and (2) its sharpening (especially output sharpening) is inadequate (it has no plug-in infrastructure). So, following the advice in the new LL tutorial on printing, I do nearly all of my image adjusting in LR and go to PS to sharpen (with PhotoKit Sharpener) and print. For that much, I think CS2 is entirely suitable, and I haven't yet upgraded to CS3, nor do I see a need to.
So, my advice is that if you don't want the cataloging features of LR and are going to sharpen and print in PS, you should just upgrade to CS3 so you can use ACR4.1 and then use a Bridge/PS workflow instead of a LR/PS workflow.
If the cataloging features in LR are OK (they are for me) and you're going to sharpen and print in LR (which is outstanding for printing--it just doesn't have soft proofing), then LR is a great choice. Generally, LR is the tool when you want to treat lots of images in assembly-line fashion (e.g., weddings); PS is better when you want to, and can afford to, spend time on each image.
It's a good bet that LR will have soft-proofing before output sharpening. Jeff Schewe hinted at that in the tutorial, and they just vastly improved the sharpening in 1.1 already. Eventually, LR might have both, at which point there will be no need to ever go to PS unless you need non-parametric (pixel-by-pixel) editing.