I have a very fast multi-core system, so I was puzzled because Photoshop always opened even tiny images slowly, sometimes taking 5 or 10 seconds, and freezing everything in the process.

Thanks to a post on Cha2e.com, I found the cause: printer drivers I don't even use!

Chase suggests checking your printers to find any offline or unconnected ones. I did not have any offline printers, but I have a lot of virtual printers, including one called "PurePage," which was installed by Thesis courseware software. That was the only one I don't use regularly, so I deleted it. Photoshop sped up immediately - small images open instantaneously now.

Other possible causes of photoshop slowdowns that I've found include: