I read The Probability Broach in 24 hours this past weekend. It was an entertaining read, but somewhat awkward and dated. Written in the late 70's, the awful fate awaiting mankind in the next 20 years was government oppression in the name of energy conservation. Obviously this never came to pass, invalidating the author's argument as to why his alternate universe (the other side of the Probability Broach) is superior.
The alternate world is strictly libertarian. George Washington was killed in that universe for proposing taxes, and the Whiskey Rebellion succeeded. Everyone wears guns, has flying cars, and the monkeys and dolphins talk and vote. It's interesting, but not particularly convincing. There's almost a complete lack of government, and no taxation, but Smith never explains where the money to pave the streets comes from, or how the fire department is funded. I can appreciate some libertarian viewpoints, but this is just a little too absurd.
The book does pay homage to Robert A. Heinlein a great deal though, in the alternate history he's an Admiral, never having caught the tuberculosis he was stricken with here in the real world. There's a "Heinlein City" in Alaska too. The most subtle homage was in the name of the mathematician who discovers the broach. Her name is "Deejay Thorens" and is an extremely thinly veiled version of "Dejah Thoras" from Heinlein's "The Number of the Beast". Unfortunately for Smith, his work doesn't hold up well against Heinlein's, on a pure storytelling level.