When would it be appropriate to record at 96 kHz as opposed to 48? Would it be overkill for video purposes, i.e. DVD? for music concerts?

First, not all systems have the overall frequency response to make use of 96 kHz. Assuming that you can actually record above 20 kHz, the best use is for sound design recordings. You might record an elephant roar and slow it down by 50% for your dinosaur sound. By slowing it, the source at 30 kHz now becomes 15 kHz. It can keep slowed down material from sounding dull.

But for normal dialog, stick with 48 kHz.

For most prosumers, 96 is just an experiment then they go back to 48.

Cheers.

When would it be appropriate to record at 96 kHz as opposed to 48?

when you're going to make multiple ad/da conversions in post. for example, you are mixing on a nice digital console like a tascam dm-3200 (like me) and have a stack of amazing analog eq's, comp's, etc. (unlike me, lol) and you want to use them during mixdown and mastering.