everything under 600hz need to be in mono, otherwise the tune will suffer when etched to vinyl or played on a mono system.
as mentioned above, its good idea to have hi hats and cymbals wide, since they mostly live in the higher frequencies. if you feel that a lower element needs to be wider, snare, toms etc, you can do that with their effects. For example, instead of panning the actual snare, keep it in mono, then send it to a stereo reverb and cut all the lows of it, so you get the powerful mono lows, with a nice wide top end.
well, on the dancefloor I can't hear much difference between mono/stereo then, but I think in productions stereo imaging does let your mix breathe a lot more and gives more space to sounds and their frequencies (if only through a gentle reverb). the problem to me is that a lot of people have their stereo spectrum too wide so the whole mix sounds out of place. Stereo should be done very gently, especially in dnb where the most important elements (yes, and I do mean the drums and bass) are mono and the rest to sauce it up (whether panned or not). props to gordo for the well advice!
make sure the samples are mono and the effects you use aren't stereo. eg if you put reverb on a mono sample it becomes stereo unless you use a mono reverb. regular drumsamples can be easily converted to mono with a regular wave editor, but most sequencers can do this internally I guess. Also make sure your tracks where you put the drums are mono tracks (like in cubase). hope this helps!