It's technically an "Open Beta," but PlayStation Home features major security vulnerabilities that hackers have already exploited. The first, seen here in blurry video, allows you to play, say, Pineapple Express on Home screens.
Using Apache and DNS redirection (simple stuff), you can point your own version of PS Home to display movies, text and music of your choosing. That's fun, but fairly harmless.
Another hack allows for the downloading of any file you want, like someone's user profile or avatar, while the final two, and most worrisome vulnerabilities include uploading any file to the Home server or deleting any file from the Home server. That's about as bad as security can get. [StreetSkaterFU and PS3Hax via Engadget]