I love Cisco fast etherchannel. Over the Christmas break we turned up a second fiber link between our two buildings here in town. When we built the second building I made sure that there were two six strand fiber pulls each in their own interduct and that inside one large interduct under the ground between the buildings. So bond one pair from each pull and you have a pretty good chance of the link staying up even if they snag the main interduct with a backhoe. Not to mention with dual supervisor cards in the main 4506R we bonded the first gig port from each sup card to make this channel. So basically if a card goes, we stay up. If a gbic burns out we stay up. And if they partially break the fiber in the ground the odds are we stay up. And in the mean time we get the benefit of both fiber links being active. By default it is load balancing by source IP. Sort of a round robin deal.
Early in 2008 we are going to mount up a wireless bridge and set it up with spanning tree values to stay down unless the entire fiber bonded link is lost. Pretty cool.