Hi,
For reference, the LP2950 has a maximum specified drop out voltage of 450mV @100mA load and 80mV @100uA. But like I said, for this application, I don't think using a linear regulator is a good idea.

The quiescent current of the regulator alone (the LP2950 that is) is 75uA which isn't much but it means that the regulator alone pulls like 50-100 times more current than the PIC does when it's sleeping.

/Henrik.