Just to add a bit to what Mary said, Uni rigs will always point higher than a sloop rig.
The jib is constantly trying to backwind the mainsail. In order to accomodate the jib's attempt to backwind the main, the boat must be pointed off the wind more.
This can result in more speed, but less pointing ability.
All the above is relevant to close-hauled sailing.
Off the wind the uni will sail much deeper than the sloop, but the sloop will sail much faster, and higher course.
Confused?
Good, I will stop there and let someone ask more questions.
<img src="http://www.catsailor.com/forums/images/graemlins/smirk.gif" alt="" />
Rick