If we don't have a book, we can probably get it for you. The main caveats generally are that, firstly, some other library has to own it; secondly, they have to be willing to send it; and thirdly, it can't cost us an arm and a leg. Some libraries don't do interlibrary loan, or do so on a limited basis, especially because of the third factor, but also because, depending on the library and the population of patrons using it, the demand may be overwhelming for their available staff. For large libraries, though, and especially academic libraries, interlibrary lending is just part of the deal.
The process is much more streamlined now than it used to be. Even the libraries who don't have specialized software - even if they don't participate in WorldCat themselves - can use WorldCat's public interface to try to locate materials. OCLC's database of library catalogs is a huge step up from the old union lists and printed catalogs for finding materials from another library. There's many fewer incidences of just phoning around trying to find something. Requests no longer come in via teletype, and although we haven't completely moved away from paper request forms on all fronts, electronic requesting has by and large taken over. And if we do have trouble finding something? There's a mailing list where the desperate can plead their case for you, their patrons. (It's used for a lot of other discussion, sure, but "Please help!" requests are daily occurrences.)
Anywho, there are things you pick up on after a while doing interlibrary loan. Some of them are intuitive, and sometimes you get surprises.
- Just because only three libraries own something doesn't mean one of them won't send you their copy.
- The mail doesn't lose nearly as many things as you worry they will. Depending on your volume, something is probably going to get lost, but for us it's about an item a year, and sometimes it's not so much lost as it got eaten somewhere by the mail processing machines, and you at least got the digested remains back.
- Textbooks aren't going to come back till the end of the semester. Sometimes this is okay - that chemistry text from the '90s? Yeah, sure, I hope your homework problems match up.
- Invoices are sometimes the best thing you can do to help your borrowing libraries get things back from their more stubborn patrons. (I know they tend to work on ours.)
- Ranganathan's Laws really do apply. Books are for use, and if copyright allows, hell yeah, I'll scan stuff out of our historical collections, but a lot of it's too rare or fragile to leave special collections and go through the mail or a parcel service. It's not that we're the only holder in OCLC; it's that it can't be replaced anymore because we're the only copy outside the nebulous world of private ownership. That's probably why you're asking for it from us.
- It's usually pretty obvious when a library is desperate to get an item from you. When a library places a request for an item from another library, they select five to fifteen holding libraries for the "lender string." When you're not the Library of Congress, which one requests items from by listing it as all five target libraries, and your library's symbol is the only one in the lending string, be it once or five times, you know you're probably their last resort.
- Some packaging supplies, while effective, are particularly annoying for folks who regularly mail books. Some padded envelopes use shredded paper as the padding between two layers of heavy paper. This is fairly effective protection, actually, as long as the package doesn't get wet. Unfortunately, the inner layer is vulnerable to the corners of books, which results in pulling a book out of a bag, only to find it infested with pulverized paper fluff.
- Speaking of mailing supplies: Tape over staples as a method of closing a mailing bag is bad. Effective, but dangerous.
- LVIS is awesome, but if you're the only LVIS library that lists your holdings for a moderately expensive journal in OCLC, it's going to be your #1 requested journal.