Re: Philidelphia Airport
"Can't say for certain if you have to re-check your bags in the normal departures hall, but you will certainly be able to leave the "airside" yourself to meet up with your friend in the depature hall."
There's a seperate, airline specific connections facility. The security guard just checks that your bag's got a US onward connection tag and bungs it on the belt, no actual check in is required.