International flights and Priceline.com?

I've never done this but I've flown Internationally enough AND dealt with Priceline enough to know this is not something I would recommend.

Most airlines offer a limited number of international flights each day; the majority of the flights depart the US in the late afternoon or evening, so that the airline can fit the highest number of round-trips in without running into the no-fly hours on either end. Unless your trip starts and returns at one of the major US International hubs, you'll be dealing with a layover at some point. When you combine all these, the chances for missing your plane due to a delay in the first leg of the journey go up. This wouldn't be a big deal if there were another plane taking off in a few hours but if your flight to Philly gets in after your flight to London is gone, you're going to be stuck in Philly overnight.

Missing the connecting flight is a pain no matter how you purchase your tickets, but when it comes to reassinging passengers to flights, Priceline (and Expedia, Hotwire, etc) customers get the last consideration. The next day's flight may already be close to full; passengers who have booked through the airline directly get reassigned first. So if you're holding a Priceline ticket, it might be 2 days before you get across the ocean.

Buying a ticket from Priceline doesn't guarantee you'll get bumped or displaced or have serious problems if you miss the plane but it does increase the chances. Only you can decide if the cheap fare is worth it. For what it's worth, I've had weather delays that caused missed connections on about 50% of the International flights I've taken and had to spend the night somewhere unexpectedly. Fortunately I have frequent flyer status so I'm the first one reassigned but I've seen other folks who missed the original flight with me get turned away the second day, so I know it happens!

I have found that going thru the airlines is your best bet on price, and getting what you want. A travel agent is good, too-do not go thru any of the cut rate people. They can be more trouble than they are worth.