There's one thing that troubles me about DEVONthink...
It wants to make copies of everything. I don't want a database that makes copies -- I already have too many. I need a system that will maintain pointers to my information (for instance, a pointer to my Documents folder; a pointer to interesting web sites), and that will regularly update its internal information about the source of information.
When DEVONthink brings in a copy of a Word document, for instance, the formating is destroyed. It's usually illegible... and if I make changes, I have to manually import that document again.
I gather there is some support for aliases, although I'm not convinced this does what I need... or that it will keep the database in-sync with changes in the file system (what happens if I put new files in the folder, or delete files?).
Overall... an interesting idea... but I think it would be vastly more useful if it didn't try to duplicate data, but instead (much like Spotlight... but better) merely tried to classify and annotate external data.