Downloading and installing trials pending my software arriving. Actually opened the read me and found this section (not sure if this has always been there in other versions, because I usually never read these things )
"2GB of available hard-disk space for installation; additional hard-disk space required during installation (Photoshop CS5 cannot be installed on a volume that uses a case-sensitive file system or on flash-based storage devices.)"
On the website thats been modified to 'removable flash based storage devices'. They mean USB sticks and the like, not SSD drives. The OS does not know an SSD drive is an SSD drive. It's just a SATA device like a normal HD.
I'm sure they are calling OS-specific API's to check if you are accessing a USB port and if so denying it. Otherwise it would be easy to trade your copy of CS5 around to multiple computers, friends and family.
Im not sure what you're saying. You said to be careful with SSD drives. I have an SSD drive, and it doesnt come near any USB. It's a normal hard drive where the OS is concerned.