puttin lens flare into an fps game is silly... unless it's supposed to be a fps game about using a camera...
how many times have you guys looked up at the sun and gotten a lens flare? unless you mean the thing you see when the sun's light gets too bright for the human eye to properly deal with... but dont call it a LENS flare...
a lens flare is something which happens to lenses due to the imperfections (compared to the human eye) of camera lenses. so.. in a first person shooter, the whole idea is to actually see the perspective of the quakeguy. not through his lens. but i guess it just looks pretty and all the amateur 3d rendering artists seem to enjoy clicking on "add lens flare" because it looks soo pretty...
might as well add that old problem that a bright light burned up the picture and left a black mark that took a while to go away (if at all) even after the bright light wasn't on screen anymore. watch some old movies and you might see the effect i mean.