I go cool. when they pop up in the corner. like when i play fifa and I get something that says "wonder strike" or some shit. i don't go to any websites and find out what trophies a game has and try to win them. I think they implemented them to take advantage of people who have hoarding tendencies and try to accumulate everything. People do weird shit. Just look at the guys on OS trying to get NCAA 1 week early. They practically would suck your cock and pay you $100 to have the game. its all about the thrill baby.
I do think that that is part of it...particularly when you look up a fucking youtube video for HOW to get an achievement. That's pretty damn lame if you ask me. But I think the system in general isn't bad and can be used to really enhance a game. Just, most developers don't do it, they do exactly what you said: "Let's just throw shit in there to get them to play the game a lot because most gamers are basically OCD."