I've been doing this for a while (I think it comes from my dad talking every where we ever went into giving him a military discount). I've gotten a good amount of free food (appetizers and desserts mostly) just by asking for it, as well as fairly large discounts. It works amazingly well.
Yet when it came to salary negotiation for my first (and current job, I was too scared to ask for more because I didn't think I held any cards. I was fresh out of college with no internships and from a pretty mediocre school, and in an area with close to 0 software companies. I know everyone says that they won't take an offer away because you asked for more, but it felt too important to chance it. In the future however I don't ever plan on just taking the initial offer.
Fresh out of college and your first job, you didn't hold many cards. I think you made exactly the right decision. (And I'm not just saying that because it was mine, either!)
But yeah, in the future, look for a job while you don't have pressure and you can afford to be pickier and ask for more. (I did this, also.) You might be amazed at the results.
Yet when it came to salary negotiation for my first (and current job, I was too scared to ask for more because I didn't think I held any cards. I was fresh out of college with no internships and from a pretty mediocre school, and in an area with close to 0 software companies. I know everyone says that they won't take an offer away because you asked for more, but it felt too important to chance it. In the future however I don't ever plan on just taking the initial offer.