Hi,
Yes, the theory is correct but 500ms per digit seems a bit slow, it'll definitely be flickering... ;-)

I don't mean to step on any toes or anything but you DO have resistors in series with LED segments don't you? Don't connect them directly to the PIC. If you don't have any resistors you may have toasted some of the segments due to too much current.... And don't forget the driver/buffer for the common cathodes, don't try to sink all that current thru the PICs I/O's.

/Henrik.