okay, interesting thread.
if you bring a military class flashbang to a PB game you ARE an idiot. BUT, you can buy flashbangs for specificaly for paintball, at my local field you can buy them, they just go bang, no shrapnol, as they are made of cardboard.
they are usefull, more so with noobs, as it scares the crap out of them

and if you throw a PB flashbang inside a building it it does disoriantate everyone in the sense, "what the **** was that" and they turn around for a couple of seconds.
but DONT make your own flashbangs, the ones for paintball are harmless (unless you shove it up your mask)
as for smoke grenades, thaey are fun, if you have a decent one it can create a cloud, and are great for fortress assaults etc.
to make your own (which WONT start fires);
-buy a can of beans
-peel the lid of HALF WAY
-eat the beans

-get potasium nitrate/salt peter/ stump remover
-get sugar
-melt them both together in a pan until liquid (add a bit of water)
-pour liquid into bean can (3/4 full)
-sprinkle a bit of potasium nitrate on top (to help set it of)
-seal bean can with super glue
-drill/ make a small hole in top
-poke fuse in
this smoke grenade will not start fire
it will give off a **** load of smoke
it will get hot though, so dont pick it up