I need to put up a extensive set of bookshelves to take a large
collection of (mainly) paperbacks. In the past I've used a shelving
system similar to http://www.screwfix.com/app/sfd/cat/...36251&id=23466

However, this time they're to go along a single large wall (as opposed
to inside a reveal or similar).

What frequency will the shelves need to be supported? Bearing in mind
that this stuff (with the associated brackets) isn't exactly cheap.

Thanks

Edward