Grumpy_Mike:
On the other side a 3V3 output is not quite enough to register as a logic one, but most of the time it will but it is out of spec. So for the best designs you need to step up a 3V3 output to 5V.
I'm little bit confused. Did you mean, step down 5V output to 3.3v, as 5v output can provide more current than 50mA? SD cards are powered with 3.3v not 5v, right?