95% of the time, no.
They'll shrug it off.

I daresay that some mics might suffer if they have crap components (no loss really) but I highly doubt it.

Voltage is essentially potential difference and it's only potential, right?

edit: Oh yeah, and don't turn Phantom on while the signal is being sent to monitors/speakers which are turned up at all.
Your mic will still work but, hell, your speakers might not.

Only real worry with phantom power is ribbons. Could fry a ribbon.

Dynamic microphones are basically little speakers. You can feed signal into them, without much damage. Whereas, ribbon microphones act more like very low current fuses than little speakers. So all they do is blowout quickly. Condenser microphones were created for this purpose and so the only thing to watch out for are some other types that did not utilize phantom power but a different powering method instead. Some Sennheiser shotgun microphones were "AB"powered & can be damaged by phantom power of 48 volts.

No AB for me baby
Ms. Remy Ann David

Guitarfreak wrote: Does Phantom Power have any detrimental effects on a dynamic mic? Here's the situation...

If I wanted to plug two mics into a Presonus Firebox http://www.sweetwater.com/store/detail/FireBox One being a condenser and one being a dynamic. Since the box only has one phantom 48 switch, this means that there will be power flowing to both mics.

It's the dynamic I'm worried about (obviously), could phantom power damage the mic or affect the recording in any way?

Phantom power is a common-mode powering method, whereas microphones produce a differential output. These two can co-exist, so you will be OK to use a dynamic mic with phantom power engaged on the interface. Make sure your XLR cables are wired correctly and are in good order so that one conductor is not going to short circuit to the screen when you tread on the cable.