> Any problems with using the RC oscillator on the PIC16C72?  I understand
> that the frequency will vary all over the place, but has anyone
> encountered any start up or other reliability problems?

I would expect not.  While RC oscillators tend not to be terribly
consistent all the time, they extremely robust.  They start extremely
quickly, and by the end of their second cycle they are fully "up to
speed".  By comparison, cystals can have problems starting and take awhile
after startup (a few hundred microseconds typically) to be fully stable.

Personally, I would think that an on-chip RC with built-in temperature
measurement/compensation would be just about the ideal form of oscillator
for just about any application not involving a real time clock.  If done
properly, accuracy could be made good to within a fraction of a percent
fairly easily, and operation of the device from a battery can be very
efficient (since the device can 'power down' any time it doesn't have
anything to do and power up immediately when anything happens; using a
crystal to do this would require waiting a few hundred usec every time you
powered up and down.