It doesn't go into limp mode, it simply retards the spark timing so that the car will run safely without knocking on regular gas (87 octane).
As for what people think they feel, I'll point you towards the numerous people that installed spiral or "tornado" intake spacers/throttle body plates and said they produced amazing amounts of power gains for their cars when in fact they did nothing at all.
And for the dynoed results of the power gain, did they let the car run for an hour or so and let it relearn the settings, or did they just dyno after they reinstalled the fuses? If they did the latter, it may have produced high readings but only because the tune for the car hadn't had time to "settle in". The computers in these cars are funny; they requires time after you pull fuses for the computer to relearn the high octane tune. Or any tune for that matter.