kajan:
Can I really get 0-5V from a RC network?
LOL, I wasn't sure how much info to throw in there. 
Yes, the RC smoothing would only run across the range of the digital outputs, which is 0.9 to 4.2V. I suppose you could let it drift to lower voltages by letting the RC discharge, but that requires setting the PWM pin to an INPUT. You'd have to choose the RC a little more carefully, and use an OA buffer so the controller doesn't mess with your discharge rate. Set the gain so the 4.2V gets scaled up to the top rail of the OA, and you're good to go.
Or you could add more resistors to offset and stretch it into range without setting the PWM pin to an input. I think... surely this has been done before. 
If you don't mind using I2C, you can get a rail-to-rail 12-bit DAC here for $5. It can output 25mA so you won't need an output buffer, and it holds its setting across reset/power-down. This would be my preference. OA design, rooting for parts and soldering looks pretty expensive to me, compared to a $5 board. ;D
Cheers,
/dev