1) Augers are fun. For a while. Until they get stuck in the ground and require herculean efforts to extract them.
2) A neighbor who has obscene amounts of useful tools is worth his weight in gold. Particularly when tools are useful for getting stuck auger bits out of the ground (see #1).
3) In the end, all you really need to dig good postholes with reasonable speed is a post-hole digger and a good heavy digging bar. The latter is very useful for breaking up soil and persistant rocks.
4) It is an uncomfortable feeling to hear thunder rumbling when you're using the tools mentioned in #3, because when lightning is a real possibility you do not want to be standing in the open holding a really big metal spike.