I pulled a few screen captures off the video I posted of the new Up-and-Over on the Gussy Trail to show how the center log provides a little kick when you go over it.
29er version: First your chain ring or bash guard hits the log, which may throw you forward a bit. My bigger wheel has already hit the ramp by the time my bash guard hits the log.
Then my back tire hits the log pitching me forward a bit. Something to look out for.
26er version: Rick's front wheel is still on the log. This may be more due to the fact that he rides a smaller bike and thus has a shorter wheel base.
Back wheel hits and kicks him up a little.