Man, I love planting C4 on the back of the guards, then randomly blowing them up one by one (for those who don't know, you can place a marker on spotted guards as if they were a location in the map; this helps keep track of the C4'd guards, although only one at a time, since you can only put one marker).
Also, I don't know if many people knew about this, but I just realized that the kills that your helicopter gets don't count towards your own kill count at the end of the game. I haven't tried using this to improve my rank yet, but since helicopters don't hurt neither your alarm nor kill scores, they should come in handy for getting better scores (unless they get shot down, of course, which is not necessarily a huge problem, given that the helicopter gets away once enough damage has been done to it). Either way, it's so much fun to throw a signal grenade in the middle of the base before concealing yourself, and then taking advantage of the battle to carry out your objective. It works like a charm in the mission about killing the two marines, and overall it's very reminiscent of the idea of dynamic battles between opposing factions that Kojima wanted to implement in MGS4 (this makes one wonder if we'll be able to call in more helicopters at once or even different kinds of backup in TPP).
As for the voice acting discussion, am I alone in thinking that it was MGS3 where Hayter truly started to fuck up? I can't stand his voice for Naked Snake, he sounds so unprofessional, naive and dumb. I suppose that he was going for something along these lines, being Big Boss at the youngest that we've ever seen him, but the end result is just... not good.