I got a grenade headshot in that slightly depressed area at the bottom of the ladder that led to the outside courtyard in cs_tire - it bounced off the sides and I died. I got a headshot. I think I still have a screenshot of it somewhere... and it might be lurking around the forums still... probably on page a million now....
once I got three, I think, but I dont like grenades. esp. frag grenades. I like flashes and smokes for their tactical advantage, but the fact is, frag grenades are effective for far too small of a percentage to be anything more than spamming.
and I don't use flashes and smokes that much, because I never get cover... my fav smoke grenade spots are in the tunnel in dust - if you're the Ts, throw a smoke in the right-side entrance to the tunnels, so a CT cant snipe at you from outside there - you only have one angle to worry about. if you're a CT, and your team is in the main tunnel room, and the Ts are camping, throw a smoke grenade so that it lands in the middle of the outside passageway, to the left, so that you can either 1) run to the left and hide behind a box and camp there (you get quite a few people that way, esp with a silenced m4) 2) use the cover (after a few secs, and make sure the smokes going the right way) to run to the right and sneak around.
and then theres the classic smoke-in-the-Assault-vent, and the smoke-in-the-garage-doorway... although I don't see the smoke-in-the-back-door-followed-by-a-flash-30-secs-later combo much at all...
dust2, the stairs right before short A is a flash spot, and sortof a smoke spot. the doors at long A are a good smoke spot, just after that on the CT side (and on the T side) are good flash spots. in fact, all doors are good flash spots, and doors close to choke points are good smoke spots...