When I purchase a design in the Marketplace, exactly what am I buying? The gerber files, the schematic, the layout, the right to order PCBs, PCB themselves? If I want to order the same design again, do I have to purchase again?
It depends on what you ordered.
In general, you are buying a PCB, produced by BatchPCB, as if you had submitted your own Gerbers. Hopefully, the description of the board includes a link to the supporting documentation (BOM, schematic, code), or the board is easy enough to figure out (ie, a breakout board). To get additional boards, you need to order them again. You do not automatically get a copy of the Gerbers or any other files.
As for all of those projects out there with no documentation at all, you are on your own. Hopefully the circuit is either self-explanatory, or you can get some usable info via Google.
/mike
If you purchase the board for the Marketplace, what you are purchasing is the actual circuit board. No files the the actual pcb. Lead Times are still the same.