grammatical number - Is the usage of "are" correct when referring to a team/group/band?

Possible Duplicate:
Is staff plural?

It always sounds wrong to me when people refer to a proper team, group, band, etc. in plural form, e.g.:

Nirvana are the creators of grunge.

The Avalanche are on the road to the Stanley Cup this year.

To me, this sounds correct:

Nirvana is the creator of grunge.

If the name is plural, it sounds correct:

The Foo Fighters are on tour this year.

What is the rule for this? I seem to be hearing this more and more these days.