I've just written my first ever challenge fic, and I have to say it was lots of fun, even though it turned out completely differently from how I intended.  I've just posted it at hpgw_ficafest, though it has to wait for moderation before it appears.  

It's an epic poem, loosely based on a mediaeval epic poem about a quest of King Arthur to find a magical cauldron in the realms of Annwn.  This magical cauldron has three properties - inexhaustibility, inspiration and regeneration.  It is guarded by nine maidens and it 'does not boil the food of a coward'.  Wonderful stuff.  So if you're in the mood for derring-do and some very questionable rhymes, as well as much H/G love,