There's no etiquette, as etiquettes go, especially with a group of friends :) I mean, if you're friends, you'll know what gives! You'll know if folks at the table will go for a $37 or more, or if even $37 is too much already! Friends are no biggie :)
Plus, it's NEVER appropriate to pick the most expensive label if one doesn't have a clue about wines! And if one does, we're back to square one: You know if your friends are ready to pay that for a wine, or if you aren't sure, you ask outright! Friends are friends and no biggie. No etiquette, no problem :)
With acquaintances, however, there should be some good ole common sense:
- Ask if someone understands wines, labels, flavors etc
- If someone does, kindly ask them to pick the wine. If they really do, they'll know to consider that someone's having fish and others meat :-P They will also know to consider everyone else's pocket!
- If nobody has much idea, then as usual resort to the advice of the waiter (or sommelier, if you're in a pricey place!)
I think the one etiquette that's certain is don't be a show-off and load everyone with a monumental bill when you don't ever distinguish between pepsi and coke :)