Apparently, each time you access a lounge the carrier whose FFP you use gets charged (some people say US$25 or so). Don't know if this is the way it always works, as Lufthansa for example never seem to swipe my card.
In terms of carriers losing money, I think things tend to even out. If carriers do pay for their members to access foreign lounges, without getting revenue from the flight (except a small portion for the points/miles), then at least they receive it when the reverse happens to them.

Cheers, Zac

[This message has been edited by Zaco (edited 10-29-2003).]