I think I know the answer to this, but I'll ask it anyway:
My project has several relays and other devices that I expect to exceed the current capabilities of my Arduino Uno board, so I plan on connecting a separate 5V wall wart to power the devices independently front the Arduino supply.
I found out that the 5v 'rails' on prototyping board I bought (Adafruit Proto Shield for Arduino PCB [v.5] : ID 55 : $6.00 : Adafruit Industries, Unique & fun DIY electronics and kits) are already connected to the 5V pins on the Arduino, so I connect the +5V wire from the extra supply, it will be connected to the 5V Arduino output. Nominally, it shouldn't matter - +5v on either side, no current flows, but in reality, I'm thinking it's a bad idea. Am I right in this?