I just did the default install on my Macbook Air (Intel Core i7). Is there some setting during the install to specify processor architecture? I haven't told MacOS to open the application as PowerPC. The icon just appears with a "X" symbol over it (actually, more of a circle with a line through it) and when you try to open it, an error pops up that says:
"You can't open the application Photoshop CS5.1 because PowerPC applications are no longer supported".