My librarian and I spent quite a bit of time evaluating open source replacements for our ancient Follett library software. We both liked what Koha had to offer and would obviously rather use something free than something, well, not free.
However, with both of us in the middle of master's degrees, conflicting initiatives, and extremely tight schedules, neither of us had the time to fully migrate and make Koha what it could be. Then Follett stepped in and offered us one heck of a deal and it was very clear. The built-in migration tools for our legacy Follett data, included tech support, and a highly polished product with seamless integration to a variety of library databases was too good to pass up.
For us, it made sense to set aside this particular effort to make open source work for us, spend some cash, and take the turnkey solution.
Our choice of student information system was much the same. Focus/SIS and Centre are both fairly mature and, of course, free (although some vendors do exist that will handle installation and support). However, we had to weigh not only the incredible feature set of the system we chose but also our commitment of time and effort versus the cost and open source goodness of products like Centre.
Don't get me wrong; I've evaluated Centre on a small scale and it's a great product. My point is that every organization needs to evaluate where open source (and therefore self-supported) software fits in. For us, we're slowly migrating to open source desktop applications and getting students and staff familiar with alternative operating systems. So far this has been well-received, but we'll stick with X2 and Follett for our mission-critical applications for now.