One possibility might be to have a limited series of Tags that each question could be linked to. For example "stepper motor", "serial comms". Stackoverflow uses a system like that.
I thought there was a post on this thread by POWTAC...
As far as I recall POWTAC's post was very short and was a useful cross-reference between similar discussions in two places.
I don't understand why it was removed.
And I thought my own reply was rather longer...
...it really only makes sense if it is seen as a response to an attempt to set up another forum for Arduino stuff.
Have you guys heard of http://www.discourse.org/It was started by Jeff Atwood from Stackexchange.comI don't know much about it yet, but it does look interesting as a new take on forum software.