In a discussion about 70's TV recently, this show came up and, since then, it's crazily-catchy theme song has been stuck in my head. I remember watching this show in re-runs as a kid and I think my favorite part was the opening credits with all those fireworks and the soooo 70's song.
The real show was an anthology series in which three love stories, all unrelated, were told with "silent movie" breaks between each one. LAS is famous for being a place where TV pilot scripts went to die. However, in one very famous case, there was an episode that Garry Marshall wrote and directed called "Love In The Happy Days" about a model 1950s family and their lovestruck son, Ron Howard as Richie Cunningham. That episode, which aired in the winter of 1972, had the good fortune to come out just before "American Graffitti" (also starring Howard) became a big hit, kicking off a wave of 50's nostalgia.
Here's a clip of the opening of the "Happy Days" pilot that aired on "Love American Style". It's interesting to note that Richie's mysterious older brother is a character in this show and his father is not Tom Bosley and his sister is much younger and not named Joanie. The show's most popular character, "The Fonz" is only a gleam in Marshall's creative eye.