As I have said many times before, I like free links in note-taking applications. In other words, if you want to create a link to another note or article, you put "[[" "]]" around a word or phrase, like, for example "[[Bertrand Russell]]". This approach allows you have control over what will become a link. Many wikis work that way, but there are also such applications as MS-OneNote, Notational Velocity, and nVALT that allow you to do this.
The second best method may be auto-linking as it is found in applications that transform any word or phrase into a link, if there is already a topic or file that has the expression as a title. It's very convenient, though sometimes you may not want a link. Take the word "problem" for example. You may not want every occurrence of "problem" in every file or topic to link to the specific problem discussed in the topic problem. This happens more often than you might think, but perhaps you would not be bothered by it. I would be, as I like more control over my knowledge base.
Another thing is that while it is easy to link to existing pages, creating new pages is less easy. DEVONthink seems to make this process as easy as it is possible. It allows you to select a word or phrase, copy it (⌘ C), and then open a new note "with clipboard" (⌘ N). You then have to manually go to the newly created topic. I am sure this process can be automated and reduced to one key press with TextExpander and AppleScript. Perhaps a template could also be devised. So, it might in the end be just as easy as enclosing an expression in double brackets.
The expression cannot be enclosed in any kind of bracket, as this makes linking unreliable. It is also important that the words or phrases are in the same case as the file. And there may be other problems with punctuation that I have not yet discovered. Another problem is that when you rename the note or article, the link will be broken. In a true wiki, the expressions linking to it would be updated.
Still, the automatic links do impart a rudimentary wiki functionality to DEVONthink. But, at least as far as I can see now, there is no capability of automatic back links in DEVONthink (or rather inDEVONnote, for which I have a license). And this makes a more extensive use less attractive for me than it would otherwise be. But others might feel differently about this—especially because it allows notes in RTF and Text format (and it is largely WYSIWYG).
1. I am grateful to a reader of this blog who pointed out this capability in a comment to Note Connections: "DevonThink will automatically create links when you type in the titles of other pages. You just have to turn on the WikiLinks option under Preferences > Editing (and click the button for "Names and Aliases"). This works on plain text as well as rtf documents." I am sure there are other things I have overlooked, and I would welcome any comments that set me straight.