Bragging rights for gamers, more software sales for developers.

They exist solely for that sweet, sweet self-satisfaction you feel when you achieve all possible achievement points for a respective game.

Have a seat, this might shock you.

Really, sit down...ready?

They're there to make you feel like you achieved something.

*falls over in shock with you*

The PS3 has these as well, although only for newer games.  The just give you goals..some of the achievements, maybe 2 per game, are for bragging rights.  Next-to-impossible to get achievements.  Not all games have them either, but games that have them are smarter for it, especially if it's a decent game.  Makes people not just want to beat it, but play it until they can tell their friends they did the unimagineable.

I don't care for them a whole lot..I like to unlock them, but the majority of the achievements/trophies aren't supported over online play, which is the primary venue through which I play video games, so I enjoy unlocking what I do, but never try to unlock them all.

They give you goals, so you can try to achieve cool things (like killing over 50,000 zombies in dead rising)

They make you want to buy the Xbox 360 version of the game, if it's multli platform. Just knowing that you get more out of the 360 version and the other version are lacking it, it make you think the other version are gimped somehow.

For some reason when I play a game without achievements now, it feels like I'm wasting my time. Nobody is going to know what I did and I get nothing in return.

I'm not really that heavy on getting the achievements, but just knowing that they are there makes me feel ok with playing it. It's like the game gives me some love back after I spend some time with it. Without achievements it's like you date a girl and keep on getting her stuff, but she never gives you anything back in return.

I do like to peak at all my friends achievements and try to 1up them, just to make myself think I'm better than they are.

I know there are a lot of games that I have that I want to beat without achievements, but those end up being put on the back burner.

Yea, nice responses. I clearly wanted to note. I play my games throughly to enjoy myself. After I finish the game, I then go back if its a good game. To play through for achievement purposes. Other than that, achievements is something for me. It makes me buy the Xbox 360 version of the game over the PS3 or the Wii version.