My experience is that you need to look into YOUR OWN MBPs hardware list and see for yourself what your NEGOTIATED SPEED is on the links. My MBP has SATA 3 on both channels, and both are running at 1.5 Gb. Some people with the same MBP have a negotiated speed of 3Gb on the HDD side and 1.5 on the optical drive.
To determine this, go to the apple icon, about this mac, more info, select Serial ATA, then look at the (on mine) Nvidia AHCI and see the Link Speed and Negotiated Link speed. The default one shown is the HDD, you need to click on the other AHCI channel to see the optical drive specs. This will help you determine where to put the SSD. I've had the SSD on both channels (since my negotiated link speed is the same on both) and had no problems. I finally bought a larger SSD and put my optical drive back.
Since you are asking somewhat basic questions, take our advice and put Lion and all your apps on the SSD. You will quickly become spoiled at the lanch times of built in programs, and want everything just as quick. Trust me on this (been there, done that, fixed it) I kept all my programs on the SSD, and all my documents, music, pictures on an HDD, and the difference in response was dumbfounding.
My experience with any CS product is that they create enormous amounts of temp files that need to be placed on the SSD. 64GB should do the trick, but if you run out of room, your second scratch disk (the HDD) will slow the application down immediately.