I got thrown a real curve ball today at work from one of our Technical Solutions Architects. He was querying if they moved 200Gb worth of files from a file store into SharePoint how big would the SQL 2005 database be?
I found a TechNet post that links off to various articles around capacity planning. This one seems to be most relevant to content storage.
Bill Bauer has a great post describing how he's managed some fairly advanced MOSS 2007 implementations database growth by moving, repartitioning etc.
Joel Olsen also has a nice post on this and links to a CodePlex project to setup mock sites to test capacity. He also wrote this back in March too.
I've also seen this one before, but it covers performance based on the size of the SharePoint install. This basically highlights that to get the best performance you need to use a folder structure within a document library if you're going to have a lot of files in there.
Why use SharePoint Document Libraries?
Whilst searching I found a great article from Joel Olsen (I don't think I've ever read an non-ground breaking post from him!) about pros and cons of using Document Libraries over traditional File Systems.