Anything.
Your example code right from the product page posted will just show as cleartext.
[easyreview title="An (optional) title goes here" cat1title="Category" cat1detail="Create up to 8 rating categories, more than enough to accomplish most review formats." cat1rating="3.5" cat2title="Sound" cat2detail="While voiceovers were charming, the game really lacked in the variety of sounds, and the music was repetitive." cat2rating="2.5" cat3title="Gameplay" cat3detail="Where the sound and graphics faltered at times the gameplay is outstanding." cat3rating="4.5" summary="This optional summary is automatically calculated. You just provide the text."]
If i posted that on my site, it would show up as it does here in the forums, cleartext. The plugin doesn't seem to pick it up (it is active and all other plugins were disabled to test).
Running latest wordpress - 3.4