BOV Pros and Cons

[collink]

I know that our Mk3's are MAF cars, so as soon as air passes through the MAF, it's accounted for by the ECU. Are there any adverse effects of blowing off that metered air? Obviously it should make the car run richer when you shift, as it's already dialed up that fuel, but I can't imagine that unless you're on it, it'll make a difference. And even then, it should burn off almost immediately, right? I've also heard there's a way to swap from MAF to speed density...does anyone know anything about that?

Thanks,
Collin