Johan, have you thought about adopting the Amazon Honor System for this site? Basically, it is a system where people can voluntarily make small payments/donations for a site. So, basically, you have an additional source of revenue, which can hopefully offset advertisements, but not require a mandatory subscription model.
I'm sure that many dedicated airliners.net members wouldn't mind donating a few dollars to see this site continue to grow, at the same time, without having too many ads.
What does everyone think?