Looking into plugging a massive LED array into the Vin of the Arduino, I figure I would look into the current limits, if any, on that pin.
I stubbled upon the Ruggedduino from a very well written blog post on 10 Ways to Destroy an Arduino. I’m considering buying one. First because I do a lot of Arduino work in the evening (when most errors happen and most bugs are introduced). Second because Applying more than 5v to the 5v pin on the Arduino can potentially damage your computer’s USB port. Getting a Ruggedduino as a main experimental board might not be a bad idea.
So getting back to the Vin max current. The Vin pin on the Arduino is directly connected to the power supply. So you are limited by the power rating of your power supply. Other limiting factors are a diode rated at 1A and the traces on the board which are rated at 2A. So final answer, under 1 amp please. This electronics stack exchange answer cover it.
Another thing to consider is the fact that the Vin pin is after the polarity protection diode of the board’s power input. This mean you are directly connected to the Arduino chip and you can potentially destroy it if you reverse the polarity of your power input. This short article on Fork Electronics covers it.