i would say leave the file asssociations with preview, it's useful when you just want to see an image without opening up photoshop all the way. instead, just get in to the habit, like i do, of using the dock as the decision for what program to open an image in.
simply drag the image onto the icon on the dock, and that program will highlight to show it can open this file type, before opening the image. it's usefull because i can look at an image in preview, edit in in photoshop, then animate in flash, test in Quicktime, drop that onto imageready, optimise it as a gif, and then test that on safari and firefox. - i choose the file associations without changing anything.