Hey, if we're all proficient in english, why not use english instead?
Makes it more open to others who aren't (yet) proficient in dutch.
If you can't think of people who could fall into that category, foreign visitors, fresh immigrants, americans 
(I kid, one of my friends is an american (immigrant), he speaks dutch remarkebly well! though I haven't posed him the S'gravehage conundrum yet).
I suppose you do have a point.
Personally I'm not a fan of holding a workshop in the hague.
I'm from way up north (friesland), and theres bound to be more people in the south.
Something a bit more public transport friendly would probably be the best bet to get a larger crowd. Utrecht, amsterdam, cities like that are fairly central (both by car and train) and would probably be easiest for people to reach.
It'd be quite a treck for me, but I might be up for it, depending on the date and location.
@robtillaart: something specific... well, I'm interested in robotics right now. And while I can figure out the schematics, I'm not even proficient in geussing values for things like capacitors.. or even resistors (which I should be able to figure out..). So for making any sort of circuit, I need input from someone with a little more electronics related knowledge. Now luckily, since I'm still a student (4th and final year though, soon doing my graduation internship).. I have access to a well stocked and equipped electronics workshop with accompanying teacher who can help me with that, but I'd like to learn to be able to do the simple stuff myself. Mostly in the domain of putting other IC's in the microcontroller circuit.