to everyone else out there, believe me, they don't always drop straight down, there are other forces present in some situations that are more forceful then the gravity.
yes, they might go down, but go to the either side or back toward the root ball while going down.
This can trap a foot, a leg or your entire body.
( a logger friend of ours got his body crushed by a leaner he tried to cut; it didn't just go down, it shot to the side and down, right on his chest. His son was watching)
I tried to draw one scenario here.
pinched limbs in a crotch, tries to make the log spin, but the root ball is too heavy. Plus add a heavy side limb, hanging in the air.
If you stand on the right side and make the cut until it falls, you are likely going to get a suprise, a smashed foot or leg.
There are tons and tons of scenarios where they don't drop straight down.
If you don't know for sure, make notch cut or a snap cut, pull with rope, use a pole chainsaw to finish the cut or all of the above.
Sometimes, if the tree it hit, is pushing back so hard, nothing will happen even if you finish the cut somehow. These can push back toward the root ball a bit if you get it to release. That's why I did a notch to the side and back cut; then used a rope to release the leaner in "rope rigging II" video.
http://www.youtube.com/watch?v=LVZkpSBKnkM