The website for Puzzles Bar, shown in this episode, is real. You can access it at puzzlesthebar.com.
The Puzzles theme song is very similar to the Cheers theme song.
In the flashback scene where Marshall learns that "more is merrier" the young Marshall is wearing a purple jacket that is supposed to be a Minnesota Vikings jacket but says Kamloops [British Columbia] on the back and has a patch on the sleeve that says Chilliwack [British Columbia].