So I had the GPIO diagram upside down (haha). SO I connected the 5V Power pin on the header to the 3.3V Power pin on the GPIO. It was only for a second or less. My RPi still works fine, but I wonder if I should now consider this board suspect?
Did any of the magic blue smoke get out? Also, what was on the other end of the lead that you were connecting to the RPi's GPIO Header? Those supplies on pins 1 and 2 (the end away from the Ethernet/USB connectors are normally to supply power to connected hardware (but the 5V can be used as a power input to the RPi - I have a RPi specific UPS that does that). Depending on what the connected stuff was you might have got away with it provided that the ground connections further towards the middle did not short out the RPi GPIO pins that actually connect to I/O lines on the SoC if they too got swapped over.
Perhaps after this time you are in a better position to judge. If you can come back to us you on this you may be in-line to get a rip tag for this question - as it is I guess this rates an honourable mention! 8-)