We visited Mt. Vernon in late June. It was hot and sticky, though not as hot as Virginia can get later in the summer. I rather missed the cool-ish, arid air of Colorado. We cooled off from our walk from the parking lot inside the visitor's center for awhile and watched a movie about George Washington.
After the movie, we walked toward the house, to get in line for a tour. We spent about an hour in line, during which the 3 boys had fun playing with leaves and being silly:
The tour was a bit rushed, but interesting. (Rather than your standard tour, there was just a line of people going through the house and a "tour guide" in each room talking about the room you were in). I found it rather interesting that the key to the Bastille is displayed here, having been sent to George Washington by the Marquis de Lafayette (a close friend to Washington, practically his adopted son).
I also found it interesting that, since he wanted his wooden home to look like stone, sand was thrown onto the wet paint to make the texture of the home look like stone. On one of the dependencies, I saw this chipped corner that shows how the "stone" is really wood. Also, I'd always heard about how the Mormon Pioneers had painted the pine used in early buildings, like the Salt Lake Tabernacle, to look like nicer woods. George Washington did this too; his pine paneling in the house was painted to look like mahogany.