I think it's worth it, at least once. As a youth I chose the National OA Conference over Jambo (showing my age - that only happened in '81) and didn't regret it. In '05 I was 1st ASM for my council troop and had a great time. My Webelo son is pumped because he will be 13 in '10 and can go.
The event is unique - check out the scouting.org site for a new preview video. All in all, I've personally had better/cheaper Scouting experiences backpacking in Colorado, skiing in Austria, scuba diving in Texas, canoeing in Arkansas. But Jambo is unique and I want to do it one more time with my