Great discussion fellas! Consider this:
I started in the B200 right seat program many years ago now (though I was actually a paid employee), and it was perhaps one of the biggest career boosters I can think of. Just like the other guys indicated, I was getting great experience and had a level of proficiency like no other. I would routinely practice approach after approach (which was loggable instrument currency), and learned the systems well enough to build the ding dang airplane. I was allowed to sit in on ANY class SimuFlite had to offer, and was encouraged to do so by the management. Heck, I even spent time learning complex FMS procedures with the FMS simulators long before I was ever FORCED to swallow the information with the pressure of an actual checkride for an employer. The truth is, it doesn't matter if you're a client or a right seater, there isn't any part of that building that is really off limits, and it's a great place to become a safer, smarter pilot.
Finally, in the eight months I sat right seat, I'm proud to say that I served well for some really great guys who were just too wound up to fly worth a crap on checkride day- and I saved some of their butts too (from busting the ride that is). Remeber the feeling you had when you guys knocked out your ATP ride? You worked your tails off, and the feeling of satisfaction was enough to make you call your ole' ma and pops and thank them for loaning you enough money to eat on that week you spent your last dime purchasing your oral exam guide (don't lie... you know you did!) I saw that every week!
See, even though I didn't have a bunch of time in the real King Air, you couldn't really tell, and I was at the top of my game. During my stay as a right seater I was offered around two dozen jobs, and I even interviewed for others with a greater level of confidence. You can hardly imagine the detail I could go into when I was asked to explain the electrical or fuel system in front of an interview board!
I eventually accepted a great job flying a beautiful B200 for a children's hospital, and then went on to fly for a regional. But nothing will ever come close to the experience I gained flying right seat day after day, disaster after disaster.
Jason