Previously they have given away tickets to the LOTR Experience in Boston, various Anime T Shirts, and a flatbed scanner. The next contest will be announced very soon, and it will have an even better prize than this one.
Is there a catch? Nope. All you have to do is to be creative.
Onezumi and Harknell are currently in the midst of a mini-tour in support of the webcomics field and the growth of a friendly community of artists. You can catch them this month in person at Ubercon in New Jersey, where they will be guest panelists. They have done prior dates at Katsucon, Otakon, and AnimeNEXT. They will most likely be returning this year to all of these events.