Can anyone recommend a more detailed tutorial on how to work with Devonthink than the ones offered on the website? I’m interested in learning step by step how to navigate through the software. Thanks a lot!
The tutorials are provided as introductions to features in DEVONthink. The PDF documentation manual is quite comprehensive in documenting features, options and commands.
But here’s the rub, in response to your question. The DEVONthink applications are general-purpose, flexible and accommodate a very wide range of workflows by people who do lots of different things, and for different purposes.
I’ve been using DEVONthink almost since it first appeared. I consider it a wonderful environment for the kind of work I do. I monitor the user forum every day, and am often amazed by uses of DEVONthink by power users such as korm, Greg_Jones and Frederiko (to mention only a few). I’m still learning things from others.
But the fact is that each of us uses DEVONthink in different ways. There can be no overarching tutorial about what could be done with DEVONthink, and how. Joe Kissel’s writings about DEVONthink might be useful. Try Web searches for articles and blogs about DEVONthink that exist out in the cloud. Steven Johnson, an accomplished writer, has written about how he uses DEVONthink in research.
My usual advice to new users is to start simply, watch some of the tutorials and then play with the application by creating a test database. I emphasize the word “play” because it’s the best way to begin to get a feel for how you might use it for your needs. Just capture some data into one or more databases and experiment. Don’t worry if you do something wrong and mess up an early database (you still have the original files you had copied into the database) and can learn by experience, throwing away that initial database and starting over. No harm done.
Probably the worst way to start would be by reading the user documentation from start to finish. That would quickly lead one to think that DEVONthink has an impossible learning curve, because there are so many features and commands. Don’t do that.
Play with test databases, and use the user manual as a reference for how a command works, how searches work (theres an appendix in the manual about searches, syntax and operators), how to create and edit smart groups and so on. Capture some new content from the Web into a database, experimenting with capture modes including the Clip to DEVONthink browser extension and Services captures. Think about how you might use groups to organize your documents, and perhaps tags for additional categorization of them.
You will begin to get a feel for how you can use your collection of documents.
Feel free to ask us questions via Support, at devontechnologies.com/contact.html
The user forum is a great place to pick up information and tips. Try doing searches of forum posts. You can register as a forum member, after which you can post questions yourself. You will likely get responses from others, and as you get experience, begin to pay forward by helping others.
Remember to backup your work. There are a number of ways to do backups, but the purpose is to protect your data from Bad Things that might happen, from a disk crash to a burglary or fire. I use Time Machine (included in OS X) backups to an external drive.
Amongst all the sage advice from Bill, I’d like to reiterate this one…
In the course of my Support role, I often create little one-off databases.
For example, when working with our Sync developer, I had a very small database called SyncFixDB. Its only purpose was to test various connections and log any issues.
When I’m answering Support Tickets, there are times when I’ll create a new database to try and replicate a User’s environment for a bit more accurate testing.
These small databases will eventually find themselves deleted. 
Other times I find myself making new databases to try different approaches to organization. My first year in Support here I had a single database per application we develop. At the beginning of the second year, I thought I’d try a single database housing all resources for all our apps. After copying the data from one to the other and using the new singular database for a month or so, I zipped an archive of the old one and deleted the database.
Play with it. Try this, then that. Make a database and mess around in it and delete it when you’re done. EXPLORE - there’s plenty to discover. 
Play with the database. i did it for a week - a Porsche hidden in a Volvo…
LOTS of power!
I bought the Take control book - Kissell - excellent but don´t forget that the original manual actually is very good. Informative and not written in a funny American way (sorry) but short and to the point. I like that.
I also realized after I played with the app for a week or so that the built in HELP is VERY good.
I have only discovered at most 10% of what DT can do and I already totally sold on it.
@ all: Thanks for all these useful and stimulating incentives, suggestions, ideas,…I will go for it and choose the “think out of the box” approach to discover DT 