When is a hotel really green?

I like to consider myself environmentally aware and I try to “do the right thing” when I can. Travelling, of course, is an activity that often has a big carbon footprint and as travel consumers it’s not always easy to know the best way to be green when we’re taking a trip.
When is a hotel really green?Some airlines or tour companies provide options to buy carbon offsets or do it themselves as part of the package, and a number of hotels claim to be green and, increasingly, carbon-neutral too. What really frustrates me, though, is that because there’s not yet a useful standard for saying a service or product is “green”, a lot of companies advertise how green they are.
As consumers we don’t really know if that’s true.
A lot of hotels throw words like “green” around just because they give you a choice about whether or not you want your towels washed every day. As another example, I saw a hotel in Costa Rica recently which advertises “green” package holidays.
From the package name alone, I might choose that over another similar hotel product just because I want to help the environment. When you look into the details, however, the only vaguely green thing about the package was an included day trip to various natural sites, but without any particular environmental awareness, carbon offsetting or anything.
That makes me mad. So until we have a reliable way to measure how green a hotel or tour is, what can we do? Is it mostly a matter of word of mouth feedback to establish which hotels really do act in green, responsible ways?