I jump seat back to the USA about twice a year from vacation. I've always found it very easy. But, I do my homework ahead of time and look at seat load factors (through someone you know at the airline, "almost" booking a ticket on the airline's website to look at seat inventory, etc). I travel on off days generally (Tuesday through Thursday) and in the off season of October through April. I also take a look at the airline flight schedules and pick off cities if I can. A lot of family, friends, and employees use their travel benefits too and they will fill the Delta flights to ATL for example. As a jumpseater, you are the last to board behind ANY other non-rev travelers. I try to find a city pair, like CDG-CVG on Delta that leaves AFTER the ATL flight and have had great success getting aboard as all the non-revs with priority ahead of me fill the ATL flight.
My last trick is listing for the seat ahead of time so I make sure I meet the cut off times (60 minutes to 2 hours depending on the airline). There are three ways to do this: 1) go to the ticket counter for the airline when you arrive in CDG/AMS/CHR and pay your taxes/fees for your outbound--that will create a listing. 2) Call up the airline (or use a listing tool for AA--see the ALPA J/S info) and ask for a "meal" listing, tell them you're planning on jump seating back and want to meet TSA requirements for listing in advance and use the terminology "meal listing" or "non-rev listing" as airline reservation agents understand that. Even though you are not non-revving, that meal listing will fulfill the TSA requirements or, 3) pay your taxes and fees for the return flight in advance at any airport ticket counter, or special services desk in a terminal. I generally do option 3 as it's easy, although you may find some counter agents who don't do it a lot and it may take some time. I try to find an international ticket agent if I can as they generally have done it before--note that a ticket window agent is necessary, not just any bag drop off agent.
These prepaid taxes/fees "tickets" for your potential return flight are refundable. Several times, I haven't been sure of the airline I want to come back on and have purchased two or three taxes/fees "tickets" in advance for returns from CDG and ATH, for example. When I arrive at the airport for my return flight, I go to both check in counters (always try to avoid checked bags when jump seating) and process with my taxes/fees ticket in hand. When I get back to the states, I just go to the airline I didn't fly with and refund my taxes/fees ticket.
If you want to jump seat over to Europe, it's very easy too. No taxes or fees are involved. Just go to the counter or gate and ask to list just as you would for a jump seat within the states. Just be a decent time in advance and it will work fine as you don't want the stink eye by walking up while they are very busy.
I've jump seated internationally within the past two years on Delta, United, US Airways, and American and have had no problems. Many airlines can't jump seat internationally on American, but FedEx pilots can (don't know if UPS or other cargo carriers can). One of the great perks of jump seating internationally over non-revving is that you get to interact with the crew getting permission to fly with them. This almost always results in an invitation to sit up front if the seats are available.