What tree/bush is this?

We have a bunch of these all around our property, they're just about taking over (as you can see it's encompassing our mailbox). What is it? Beneficial or not?

Are the leaves sort of mealy, and quite white/silvery on the undersides? Are there berries? If so I would guess some kind of Eleagnus. Often considered invasive but if that's what it is, it's a nitrogen fixer, fruit is more or less edible, and a good animal forage.....

Yes about the silver leaves, no about the berries.

Probably Autumnberry (Elaeagnus umbellata), aka Japanese silverberry, autumn-olive and Russian-olive. It has edible fruit that appears in the fall. Highly invasive, it has become naturalized in many areas.

http://www.nps.gov/plants/alien/pubs/midatlantic/elum.htm