Yes, a nice overview, but with a large omission. DevonThink is the bee's-knees when it when it comes to storing PDFs and any other type of text-bearing document.
Once you set up a classification system, it does all the work for you in classifying your documents and then allows for a fine grained search of your documents that not noly finds keywords, but will also point you to documents that share a "family resemblance" to the type of document you are looking for based on your key words.
The more documents you have, the better this search gets, up to a point.
From a researcher's point of view, this allows you to collect more documentation than you could ever read yourself and narrow down searches as you wend your way through the field you a reseaching. Used intelligently and not as a crutch, DevoThink can save you a lot of time.