Are you saving the adjusted JPEG files as 'ready-for-printing' or do you work further on them in CS3? If the former then fine but if you are doing further work in CS3 then I see two major flaws. One, as John as has already said, is that JPEG files are only 8 bit and compressed which means that you have already discarded half your image data converting to 8-bit (standard JPEG can't handle 16-bit image data) and then you lose further image data with a lossy compression format. Remember also that each time you open a JPEG file the PC has to recalculate (guesstimate) the lost data and then each time you close the file again you lose a bit more image data. Even at minimal compression ratios this can add up over a period of time... If you wish to work further on an image in CS3 then either export the image directly to CS3 or save in a 16 bit lossless or uncompressed format such as TIFF or PhotoShops own PSD format. I also presume that ACR is like most other RAW converters in that adjustments to the RAW file can be 'saved' to the RAW file (actually they are held in a linked file known as a 'sidecar' file) which the program will apply next time ACR opens the adjusted RAW file - NOTE the original RAW file has not changed and the shot settings can be recalled at any time.

The other is that images should only be sharpened before printing. With any file that is intended for further work sharpening should not normally be applied. Some adjustments, eg cloning or the healing brush, can show up quite strongly if applied to a sharpened image but blend far more seamlessly if the image is in it's native soft state. I also strongly recommend not sharpening the original image but create a duplicate layer and sharpen that. This has the advantage that if you overdo the sharpening you can back it off by reducing the opacity of the sharpened layer allowing some of the softer image to show through - this can even be done selectively if using a layer mask.

It's unlikely to matter whether you save from ACR or CS3 as the compression routines are specific to the file format rather than the programme used though I wouldn't take that as an absolute - another software producers programme may vary slightly.