I remember a few years ago I was listening to two pilots go at it on 123.4500. Usually the conversations are brief and they don't give their locations Well this particular time one guy said he was north of Albany NY and another guy was just about to land somewhere in Delaware. I heard them both pretty clearly!!! Definitely one of my more memorable experiences monitoring
Some good stuff here, but getting back to us folks using consumer grade equipment on the VHF air band:
At an elevation of about 800' ASL, using a Radio Shack Pro-2042 with a discone antenna on the roof of a single story residence, I would routinely hear commercial a/c 250-300 miles away at, usually, 35k~39k altitude.
My farthest catch was a NASA TR1 "above 60K" at 400+ miles.
As for airports, I lied in an area surrounded by hills, but 20~25 miles was my max.