I was watching one of the pod casts that are on this site, "The Mad Mage" and the wizard in the group said that he only needs one pearl of 100 gp value because the spell doesn't consume the pearl.  I have always thought that material components were always consumed when the spell is cast.  Am I wrong?

In 5e, Material components are only consumed if the spell says so. Prior editions of D&D generally consumed components by default.

Quote from PHB >>

But if a cost is indicated for a component, a character must have that specific component before he or she can cast the spell.

If a spell states that a material component is consumed by the spell, the caster must provide this component for each casting of the spell.

Just to provide some examples:

Identify has a material component of "a pearl worth at least 100 gp and an owl feather," as you already stated. This means that while you need a pearl worth at least 100 gp, you do not need an owl feather as there is no cost associated with the feather. You can, instead, use your arcane focus for that particular component... '

I'm actually not sure if you have to use your arcane focus for the owl feather, essentially requiring the pearl and the focus to be used together. I think RAW that would be a yes, but I guess it would depend on the DM?

Arcane Lock has a material component of "gold dust worth at least 25 gp, which the spell consumes".

The spell will explicitly state whether or not the material components are consumed.

Thanks.