Just to play devil's advocate GT, I actually get wound up if someone tries to swap a trip for my days off, or tries to take a layover off me in order for me to do their awful night turnarounds and only bothers to put it through the system.
If it's almost a like-for-like trip, fair enough but if you want to do my WAW and are offering me a night BEY or that s*dding night AMM (that would be a 330 special, gents), text me and explain why! If you're trying to fly relatives home, or need to be home for some reason, most people I have spoken to will be decent and help you out, even if it means giving up a day off - not that it'll help soon of course.
It's only polite - eSwap is, for a lot of people I have spoken to, perfect if you can't be bothered to actually speak to your colleague!
Also, don't you HAVE to check your company email in order to know somebody's sent you a request?!
And as for paying for flights, it's a sad reflection, and a real reflection on the mentality that pervades life over here that your colleagues will only help you out if you pay them.
Rant over.