Diminished chords are pretty cool once you figure out how to use them, and the scales that go with them. A common way of using them is to incert them in between 2 chords whose roots are a whole step apart, ex; G7 G#dim7 A- D7, check out Fats Wallers Ain'tMisbehavin for a good ex of this.

You can also take a dim.7 chord & slide it around on the neck of the guitar in -3rds. Check out the Beatles song Michelle for this idea (it's a great chord prog.)

By the way Christoph, an easier way of thinking of the formula for a diminished7 chord is to take the Dom7 chord & sharp the root-you may already know this stuff, I haven't veiwed the lesson yet.