Make your FireFox think it's a PSP browser.
Heh, as soon as I saw the news of the Rachet and Clank demo, I immediately thought of this.
This simple little trick will allow you to access any PSP-only site and sign up for PSU's beta's that must me viewed through a PSP's browser.
NOTE: This works on FireFox only! (any version)
1. Press CTRL + T to create a new tab
2. Enter about:config into the address bar
3. Right click anywhere in the white screen
4. Click New-> String
5. Type the following into the dialog:
6. In the value dialog, enter the following:
Go to http://pspbeta.us.playstation.com/ and sign up for the beta using your FireFox!
Mozilla/4.0 (PSP (PlayStation Portable); 2.81)