Okay, something that bugs the fuck outta me about games: collectibles as replay value, or worse yet, necessary bits of story. It just reeks of poor design. I'm sorry, but if your game's only replay selling point comes from "ZOMG 100% COMPLETE, GUIZ!" I'm not gonna bother replaying it. Not everyone gives a crap about finding every little bauble or meaningless bit of paper in a game, not everyone wants to spend hours on end hunting for crap because they're extremely anal and don't want to miss something important.
Also, if you do that crap, and only give certain bits of critical plot detail thru them, then I'm not gonna give a shit about your story. However, if it gives details about the world at large, maybe a running secondary dialogue that, while not plot critical, is nice to have, then its cool. A good example of the latter are the recordings from Dead Island. They're not critical to the game's overall narrative, but they help flesh it out and give it some added depth. Hiding critical plot details from players because they're simply not meticulous achievement hunters is a terrible way to design you game's story. Explain it thru backstory, dialogue, or even an internal monologue. All of those are far easier to accomplish, and don't unnecessarily punish players for not being anal enough to check every nook and cranny for your hidden bullcrap.