RandyMac is right there would be a lot of surface area, but on the other hand, you wouldn't have to worry about 'em rolling down the side of the mountian.
Newguy18, for directional felling, it doesn't matter whether they are round or square. The same principles would still apply. You would just need to REALLY consentrate on your depth of notch. Haven't you ever felled a flat sided tree?