(Old post, but someone might find this useful)
When hops are left out, heat up etc. they oxidise. In some hops this can reduce the desirable aromatics, but in others it just changes the aromatic properties, or even improves them. I don't know any off-hand, except Cascade smells like fizzy sweets when fresh, but Grapefruit when oxidised.
It's all about the levels of cohumulone, lupulin and what have you.
Read Ray Daniels' book 'Designing Great Beers' for loads more on that!
And no, I'm not Ray Daniels.