LibraryThing works great for inventory purposes, especially with a library as large as the querent states he has. (I personally have over 2000 books entered into LT at this point.) Using tags for location purposes is another great idea, and there are a good many LT users already doing that. As for open format, no, the software running it isn't open, but a CSV datadump of one's personal library is available. I have a spreadsheet on the home computer and on the PDA so I can make sure I don't buy books twice.

However, the poster's still going to have a mess of books. Taking them all off the shelf to catalog the things is a good start, but he needs to know where to find them. I'd sort them on the shelves by subject matter, then size, then by author and title. Then use LT or whatever tag-supporting cataloging software to tag locations of the books once they are on the shelf.

I admit I was using OpenBiblio before, which does meet the OP's requirements for an open program and will do all those nifty cataloging and locating things except, perhaps, for cooperation with the barcode scanner--but it's more for actual library use and may just be a bit too in-depth for your home user.