-Pop a front wheelie and land the large chain ring on the log.
-You should land with the power foot forward, about 70 degrees.
-Shift your weight forward and pedal.  Not too far, or you might crash.

For both H) and I), some added:
Bill Rod [smts!brod@msss.attmail.com]           
I think you should add "When clearing/climbing logs of any size, momentum is 
critical.  This is what gives you the oomph to get over an object"

Dave Blake [dblake@eureka.wbme.jhu.edu]
-Do a front wheelie.
-Land your front tire squarely on the offending log.
-At the same time, move your weight forward and crouch down.
-When the tire hits the log, jump forward and throw your handlebars
 forward and down.  You jump off your front wheel mainly, but the back
 as well.
-Your chainring should clear the log, and your front wheel should land
 on the ground as your rear hits the log.  As long as your chainring clears
 the log you will have no problem landing if you go too far forward or
 too far back.
-Practice on small logs first - this skill does not happen overnight.
-Author's blab:
    -before trying this technique, please read the disclaimer!