The last issue of BBC Radio 4's costing the earth series (see
BBC - Radio 4 - Costing The Earth 03/08/2006 ) was dedicated to tourism and found that a package deal to Benidorm was environmentally better than many ecotourism packages, although they also said that of course it's better to stay more local (e.g. in britain if you're british). You can listen again at the link above, but only tomorrow (wednesday) and maybe thursday I think. I don't always find their arguments stand up too well but this program was quite good.
Regarding hotels it is nice if they're environmentally friendly but at the moment for me price is a big factor. I suspect that it makes more of a difference if you don't adopt environmentally friendly behaviours yourself as a matter of course though - e.g. it doesn't matter to me if my hotel key card turns the lights out in the room when I leave because I'm likely to have done it anyway.
Off the top of my head I'd like to see water saving devices in the bathroom, the option not to get towels washed every day, energy efficiency, double glazing and adequate natural ventilation....