If you haven’t checked out SparkFun Electronics’ prototype collection yet, you’re missing out. They unearthed many of their old prototypes and published them to show what kind of mistakes could be made. You’ll see plenty of errors and get hints on what to look for while developing your own hardware. This pairs well with their Design for Manufacture post. Along with the pile of broken board iterations, they also walk through how the company developed. Finally, they specifically cover the individual iterations of the BlueSMiRF.
One of the interesting modules in the gallery that never saw full release was the SparkFun Toys line pictured above. The individual units used the standoffs as the power and data bus. The four posts were arranged so they could only be connected in one orientation: power, ground, TX, and RX. It’s an interesting idea that seems like it might be worth exploring further. SparkFun says that it worked fine, but didn’t feel they had the resources to market it to the intended audience.