If we are bound to have user-created prediction markets (Foresight Exchange, Flutter, Inkling, InTrade, etc.), then, by the same token, we need an appropriate ranking methodology to present only the most interesting (and urgent?) contracts to the frontpage readership.
Just for your curiosity, see this Digg-equivalent FAQ, and make sure to give a look at this new site —via Jason Kottke. Compare it with Digg and Delicious —and maybe SlashDot. And, now, ask yourself: Which ranking methodology would you use to improve this prediction market home page?
We are not all forward thinkers.
As for the frontpages of the prediction exchanges relying on user-generated contracts, they could borrow one rating mechanism from one social bookmarking service, or they could outsource that to whichever social bookmarking service each user usually trusts. (That means linking from the exchange frontpage to the best social bookmarking sites —probably an idea that exchange executives won’t like.)
See also my other comment on how to improve the social bookmarking sites:
http://www.midasoracle.org/2007/01/27/very-popular-social-bookmarks-for-prediction-markets/#comment-795