I know this is probably a REALLY dumb question. But is there any actual reward for amassing achievements or is it more of a matter-of-pride situation? I've vaguely heard of "achievement prizes" but I have no idea how they work.

mostly for the lulz.

Some Achievements will give you an item or a forum title if you complete them. How you actually trigger the Achievement prize upon completion varies quite a bit, and may need some fiddling by you.

some achievements give rewards or prizes, which can be seen on the achievements page. if there is a little orange star next to the counter (the 0/1 or whatever number it may be for that particular achievement), that means it gives a prize. you can click on the star to see what the prize is - it could be an item, or a forum title. other than individual achievement prizes, the only incentive to amass achievements is simply for the pleasure of having a lot of them, just like achievements in any game.

thanks !!

you are welcome