Your data will be displayed as a hierarchy of folders, just like the Finder. If you've dragged in your entire Documents directory, its structure will be faithfully recreated within DEVONthink.
DEVONthink is very good at finding things within this large pile of information. The quick find box in the toolbar offers a variety of search options and can zip through even large databases with impressive speed.
F brings up a separate search window that offers much more power. Enter a search term; but before starting the search, try clicking the Spelling or Context buttons. These open a drawer with a list of additional search terms that DEVONthink considers similar, either by the way they are spelled compared to your search term, or by the context in which they appear within the database.
Double-click one of these suggestions, and the search is done on that term instead. Thanks to the way the search window is designed, you can view the document you find before opening it.
Another important way of finding related content is the See Also button that appears when viewing any document.
This really comes into its own once you have spent some time organizing your groups and classifying your documents appropriately.
Opening the See Also drawer brings up a list of documents that DEVONthink considers similar to the one you are viewing now. Select something from the list, and you can read that in situ, while you still have the previous document in your head. Now you can perform a See Also search on this second document, repeating the process; this is exactly what Steven Berlin Johnson described doing in his influential weblog post.
He concluded that having small, granular snippets of information was much more useful than large documents: "I have pre-filtered the results by selecting quotes that interest me, and by archiving my own prose. The signal-to-noise ratio is so high because I've eliminated 99 percent of the noise on my own."
Which doesn't mean that you can't, or shouldn't, have long documents in your database; but Johnson's identification of the 50-500 word count "sweet spot" is probably one of the best tips you can find for long-term usage of this application.
DEVONthink Pro can count the words in a document, but in more ways than one.
Sure, it will tell you how many paragraphs, words, and characters each document has, but the analysis of words goes much deeper than that.
Much of DEVONthink's thinking is done by examining concordance, or the number of times each word appears in each document.
You can examine any document's concordance with Tools -> Concordance, and detailed word count stats will appear:
From the chart, you can hit the Search button to show other files that contain the same word (great for hunting down obscure links), or the Similar button to show words with similar meanings or contexts.