Yes, and yes. I've even PAID to work the last three Jamborees on staff. Our oldest son was a participant in 2010 and loved it. Our youngest will likely go in 2013.
The cost of the Jamboree itself is around $800. This is the "national fee" for attending the Jamboree itself. Jamborees are a "mountain top" Scouting experience for most boys. The rest of the money is the amount that your local council assess as the "touring package". That is, the cost of transportation, hotels and meals along the way, and any sight-seeing costs to and from the Jamboree. All in all, your probably looking at about a two week trip (depending on where you're coming from).
However, as for "what do you do at a Jamboree", I will say that for 2013 the National Scout Jamboree will be going through a major paradigm shift. From 1981 to 2010 it was held at the Army's Ft. AP Hill near Fredericksburg, VA that the BSA rented from the US DOD. In 2010 the BSA announced that it had, through a major donation, purchased a permanent site for the Jamboree in western West Virginia. It is in the "New River" area and is in much more of a "wilderness" area. During non-Jamboree periods, "The Summit" as it is known will be operated as a high-adventure base for white-water rafting and such. All of this is going to re-shape a lot of the Jamboree experience.
Given AP Hill's proximity to Washington, DC it used to be standard for troops to send several days touring our nation's capital... but given the additional distance to the new site, some council contingent troops may drop that option (and touring costs). Previously, troops had to bring all of their own equipment... now the BSA will provide all of the tenting and troop equipment. The troops only have to show up with personal gear. At AP Hill there things were spread out and there was a transportation system (school busses), at The Summit things will be more centrally located and boys will be expected to "hike" their stuff in to the troop sites. At AP Hill the list of activities was massive such that it was impossible for boys to do everything (earn merit badges, rappel, BMX, trap shoot, SCUBA, boating, Army adventure area, exhibits, hands on science area, etc., etc.) News is that The Summit will be the similar, but the mix will change with more of a "tilt" towards "high adventure" stuff that takes advantage of the locality.
Another change is that before the Jamboree consisted of about 40K participants and staff... plus about 10K daily visitors. Visitors were allowed full access to the site and the massive arena shows, but were restricted from doing certain things like the "Action Centers" (rappelling, BMX, archery, etc.). For 2013 that is all changing. Visitors will be barred from the main campus of the Jamboree. Instead there will be a separate "Visitor's Village" with things for visitors to see and do. And while in 2010 the BSA started asking for a $10 "donation" per carload of visitors, they'll be charging a set admission fee for visitors in 2013 and I believe you will be required to pre-register.
Here's the web site of
the new Jamboree home.