Fenixp: A bit of an side-effect, sure, but handy one nonetheless.
I don't know whether you can really call that a side-effect. I mean, what's the purpose of achievements and trophies? Sure, it's about getting people addicted to games and buying them but it is tied to the social experience, you are meant to compare your skills and gaming experience with others so I think knowing how far your friends have gotten and thus what you can talk about is totally one of the social aspects of achievements/trophies that MS/Sony had envisioned.
BadDecissions: God, Silent Hill Homecoming on the Xbox. There may have been a way to turn them off, but I couldn't figure it out. Yeh these stupid achievements popups don't ruin the horror atmosphere at all!
At least Homecoming's developers designed that shit themselves, from what I've heard the most moronic implementation of achievements/trophies was in the HD collection of SH2 and 3. Those games weren't designed with that shit in mind and the company behind the port made the implementation EVEN WORSE than anyone would have imagined, it seems (and yeah, the port was done at least by some people who were involved in Homecoming).
Darvond: What would be the point of that? They're already pointless, buying one for yourself would be like buying one for yourself in real life. Sure, you can reward yourself, but you'll look as the most vain person ever.
True, but now STEALING trophies, that's impressive both in real life and gaming.
Edit: Anyway, this discussion reminds me of a thought I had years ago. I don't get why MS and Sony don't at least allow game developers to customize the Live/PSN overlay for their game, the sound that plays when an achievement/ trophy is unlocked etc.. That would make things SO much better, IMHO (and I apologize for my ignorance if that's actually already possible on some platform - haven't observed it myself yet, however). If that stuff has to be present, no matter what kind of game someone's making then at least they should be allowed to adjust it somewhat to their game.