I think member rankings/etc./different levels of paid services could also be bundled nicely with promotions in cooperation with travel partners such as airline/hotel companies...

A site like this has a lot of potential, I would say.

One thing would always have to be clear to all cooperation partners/advertisers, and that is a bit similar to the situation a newspaper is in with its advertisers:

There will be no censoring on behalf of cooperation partners or advertisers regarding what people talk about - no deleting of discussion of targeted promotions, etc.

Perhaps the payments received by the participants might even help to decrease pressure from said companies to push their agenda through and make this site a marketing and customer service tool for them where they would start to feel free to think they can censor members' postings - unfortunately, we have recently seen such tendencies already.