It would be a big big change to do, and in the context of being a NSW DET school library with all the support structures and organisation in place as part of a large education system, it's not something I'd jump into without a deal of thought.
But it's interesting to think about, to consider how else we could organise a library to make it work for our customers. There are advantages and disadvantages - as when cataloguing a book/resource, you can use several subject headings for the catalogue to help readers find it, but in the end the one physical resource has to get one shelf location (in our current system, one Dewey number); a decision has to be made on the main topic of the book, and thus its final shelf location.
Here's an article about libraries who have changed from Dewey to using bookshop merchandising style organisation. Food for thought.
One thing I wouldn't do (and have been asked for occasionally over my career) is grouping books by faculty/subject 'because it would be easier'. Sounds simple, but then it ignores the fact that the 'science' books may also be 'geography' books (eg. volcanoes/natural disasters). When I politely point this out, the teacher who is suggesting this usually looks thoughtful, and recollects an engagement elsewhere....
There are, though, plenty of ideas from bookshop merchandising that we can borrow for school libraries. Which of the shelves below would you explore for longer? These...
We don't have enough space to put all our books face out; this is one of three bookcases like this, and not all will have everything face out. But it's better presentation to encourage reading than the first, isn't it?
Article found via Twitter.
Photographs of shelving from my library's browsing area on the mezzanine: first photo with iPhone camera, second with Hipstamatic iPhone app.