The subject here reminds me the following remark since I personally use the same approach of Michael Karas for too many years since I started designing with AT89C51.

It is about the selection of the first 2 resistors at the output port (in M. Karas 2K2 and 10K).
For slow raising 5V supply, the port outputs (of some ICs, not all) might be initially at ground, up to a relatively high supply level (about 2-3V for example). In that case, if the 12V (or any voltage at the power section) is already on and the 5V, for some reason, is increased rather slowly, the end load might become active for a short period. In my opinion, that problem is not important when the final load is driven by a relay. It is likely that the relay will not respond to that rather short turning on, unless Vcc (of 8051) is deliberately increased very slowly. But for me it was once a serious problem. I was using a 4-transistor bridge (driven by 2 port outputs) to activate a 35Vdc motor in two directions. And if by hazard the mains was applied slowly the bridge became shorted with some smoke :) Therefore for critical cases, I used to choose the 2 resistors (mentioned above) as 4K7 and 1K2 (though their ratio is the most important) in order to be in the safe side no matter what the IC type is and how slow the 5V is applied.

Kerim