Feel free to use them.
You can also download the entire set here and add into your Windows Live Messenger or any instant messenger as custom emoticons.
Update (24th Jan 2010): The emoticons have been added to Viwawa Forums, MatchIt, Checkmate, Sushido, Zany Bridge, Wahlords, Numeroid, and Groword, in addition to Big 2.5. Enjoy!!