George Washington Slept Here

"Abe Lincoln never slept here—but YOU can!"

—A billboard advertising a hotel on Kentucky's Interstate 65, the "Abraham Lincoln Memorial Expressway"

On Bob and Alice's roadtrip, they come along an old roadside manor. In front of it, they see a sign saying, "George Washington Slept Here"! How exciting!

This is when an old inn, manor or other tourist attraction, was once used by a famous, usually dead, figure. Could also be anything from an outhouse to a gas station.

Examples of George Washington Slept Here include:

Film

George Washington Slept Here is the title of a 1942 film (based on a 1940 play) about a married couple of New Yorkers who purchase a dilapidated farmhouse where George Washington allegedly spent the night once. Hilarity Ensues as they try to fix it up.
In Heathers, psychotic teenager Jason Dean's father, who runs a demolition company, laments that a historical society is trying to keep him from tearing down a hotel. The reason given is that Glen Miller and his band once spent the night there.
Referenced in the film Arsenic and Old Lace when one of the police officers asks if George Washington slept in the old house owned by the two old women.

Literature

In America (The Book), among the list of George Washington's achievements is "All-time record holder for Most Places Slept."
In Mr. Blandings Builds His Dream House, one of the selling points of the house is that General Gates supposedly stopped to water his horses there during the Revolutionary War.

Western Animation

The Simpsons did it with Jebediah Springfield, on more than one occasion.
Parodied (naturally) in Family Guy. In an attempt to convince a historical society that the Big Fancy House he inherited had $50,000 worth of history occur in it (so he could sell it to them as repayment of a debt), Peter scratched a fake "Jesus Was Here" message on one wall and tried to make it look like the Underground Railroad had passed through it. This was a disaster. Then it turned out that the house had been a presidential brothel frequented by Abraham Lincoln, among others.

Real Life

Happens fairly often in real life, with old inns advertising that a historical figure once stayed there.
If we expand this to other basic activities by famous figures, you should travel to Israel sometime. They build churches, mosques and shrines on these places, most of which are historically proven to be not where the alleged event happened at all.
The page quote is from a billboard advertising a hotel in Bowling Green, Kentucky, that parodies the state's tendency to do this with its Lincoln connections by proclaiming, "Abe Lincoln never slept here—but YOU can!"
Bran Castle in Romania, at the border of Transylvania and Wallachia, has a reputation of being closely tied to Vlad Tepes, though such claims are suspect. While it is currently used as a museum, there was an attempt to sell it to the highest bidder in 2007; the auctioneer marketed it as Dracula's castle.
New York City tour guides call Fraunces Tavern, which is still there, "George Washington's favorite restaurant".
In Ireland, if there's a church or the remains of a church that's more than two hundred years old, it's a safe bet that your tour guide will claim that "The Saint Himself" (Saint Patrick) once said mass there.
After the First World War, Prussian general Max Hoffman got in a dig at his former boss, Paul Von Hindenburg, through one of these:

"This is where General Hindenburg slept before the battle, this is where General Hindenburg slept after the battle, and, just between you and me, this is where General Hindenburg slept during the battle."

In the Austrian town of Braunau am Inn, the building where a certain historical figure was born is adorned by a memorial stone carrying the following words:

For peace, freedom and democracy. The millions of dead remind us; may fascism never return.