There was a recent post on ALA Techsource that mentions OSS in libraries, among other things, that’s worth reading. Be sure to also read the comments. The use of open-source products is a large shift and may not work in every situation. It also does not rule out vendors, just certain business models. Definitely read Joshua Ferraro’s comment as he is one of those vendors.
From there you may want to read Why commercial ILS vendors won’t use an OSS RDBMS by johnvw. And again be sure to read the comment which is by one of the OSS ILS vendors.
And then go ahead and read Open Source Software: Should You Bet Your Career On It? over at Disruptive Library Technology Jester. One of the take home’s is that the problem is the evaluation of projects and not necessarily oss vs commercial. The ALA article touched on this but this one goes more in depth. The ending quote: