So as I progress with my standalone projects, I'm coming to the conclusion that I tend to have USB power available everywhere, while providing > 7V to a 7805 means a specialty wall wart. And even when I'm away from my PC, USB wall adapters can be purchased at the corner store while 7V supplies are less commonly available.
My stuff generally has low power demands (charlieplexed LEDs, the occasional sensor), so the 500mA cap isn't a problem. But I imagine it's not simply a matter of soldering a USB jack onto my board and there's my 5V and GND. So far I'm figuring on the following:
1) A PTC acting as a fuse in series to prevent a short from cooking off my USB port. 2) A cap bridging 5V and GND to smooth out the load.
Are there other best practices? Passive components I can use to ensure I'm getting the full 500mA? Additional safety or filtering components?
Or is this just a Bad Idea, and it doesn't work as reliably and universally as it seems like it should?