I just use a hoover to suck the dust out of my front fan dust guard.
This was the best I could find... the filters are actually part of the fascia so you have to remove the whole front, couple of screws and some clips which are released by squeezing the sides I imagine....
http://www.overclock3d.net/reviews/cases_cooling/corsair_graphite_230t_review/6
Well considering people design cases etc. for a living, what a rubbish design. It's not as if they don't expect the filters to need cleaning is it?