I'm by no means an expert on this LINK+ system, I've just used it at several Bay Area libraries before. I found this link on the web that explains what LINK+ is and how to use it at the Berkeley Public Library. Web Link
It seems a little different from InterLibrary Loan in a couple of ways:
1. there is no fee
2. it is done online (at home or at library computers) so it is generally faster
3. doesn't require library staff to complete the process
4. (and I'm not sure if this is not also true of InterLibrary Loan since I haven't used it) you can get books that are pretty hard to find b/c many of the libraries on the LINK+ system are univeristy libraries.
Again, I don't know what or if there is a fee for a library to participate in LINK+, but I do know it is a very useful service to get hard to find books quickly.