I'm using Lightroom 3 and Photoshop CS5, having moved on from CS and CS3 (hence the offer to "help with CS3"
). They integrate perfectly if you commit to always start in Lightroom, and you match up the Photoshop colour space to Lightroom's. While some plugins such as Perfect Resize work in both LR and Photoshop, others don't (PK Sharpener).
Now that I'm becoming more proficient with LR, I'm mainly using Photoshop just for stitching panoramas, occasional touch-up and "hacks" like blurring backgrounds. The 2 main advantages of CS5 for me over CS3 - (1) "content-aware" fill for the gaps at the edges of stitched panoramas and for removing powerlines etc in landscapes, (2) faster performance, (3) using PK Sharpener for specialised sharpening (LR's sharpening brush isn't as good IMO, but capture sharpening is ok).
Which brings to mind - one disadvantage of LR3 is that it is a bit slow to load up images, particularly if there's a lot of brush adjustments. On the other hand, I like the noise reduction, the ability to process multiple photos at once and the DAM function.
Hope this helps - tho' probably not your wallet