As someone who has been on both sides of hiring, I think this is something you absolutely should do. When a company makes you an offer, it means all the people who interviewed you got together and decided they liked you. Mentally, the company has committed to you. For the hiring manager to lose you over a few thousand dollars a year will reflect very poorly on him/her.
This is also the point where you have the highest leverage. Your leverage is always based around the idea that you might go to another company. When you're considering multiple offers, it's very credible that you might work for another company. Once you've been hired and you've been working there for a year, they figure the inertia of leaving your job and going to another company is big, and limit your salary raise.
Thanks for your thoughts on the matter, but it has happend to me. The offer was retracted based on lack of interest on my part as seen by the company - this is back in '07 when I was in talks with a few companies and most had given me offer letters.
You need to be careful with your advice to others, I know you mean well but it could really mess somebody up in a very real way.
I actually use a small tweak: rather than "all are equally good so I'm choosing based on salary," I pick the company I want, then go to the others and say "another company has offered me X. Could you offer me a little more?" Once they do, I go back to the company I want and say "another company has offered me Y. I really want to work for you, so could you match Y?" Perhaps the "I really want to you," and only asking to match another offer, is more important than I thought?
The best thing is to get the company excited about you. They get excited by knowing that a) you're awesome in your skills, b) you're gonna be easy to coach, c) you're gonna hit the ground running, and d) you're passionate about the company because you buy into the culture and mission.
My advice: go to salary.com and such sites and look at that data for that job, and tell them you are in the 80th, or 85th or 90th percentile, and why (what a typical guy in your fild does not know or what makes you exceptional).
I disagree on the threat of retraction, obviously. Most firms aren't going to risk their reputations by rescinding an offer unless there was something severe (failure to disclose a felony) involved.
However, I think using post-offer leverage to negotiate extra pay is a bad idea. The leverage exists, but it's limited. I'd rather use it to get insight into (and favor in) project allocation than a measly few grand. Project allocation is the difference between having a successful career-- learning a lot, working with great people, getting the promotions-- and needing to find a new job in 12 months. A few thousand dollars is nothing in comparison. This style of negotiation is more subtle, and takes the form of a "reverse interview" than a line-in-the-sand "I want $10k more" statement, but I think the former is better at (a) presenting yourself well, and (b) getting you what you actually want, which is a successful career.
I also tend to subscribe to the philosophy that the first 120 days of any job (including post-offer negotiation) are an extended interview. What you want to show is that you care about your work intensely and that you have the potential to reach very high levels, but also that you expect to be challenged and given appropriate work; not that you are a mercenary who makes career decisions based on a few thousand dollars.
This is also the point where you have the highest leverage. Your leverage is always based around the idea that you might go to another company. When you're considering multiple offers, it's very credible that you might work for another company. Once you've been hired and you've been working there for a year, they figure the inertia of leaving your job and going to another company is big, and limit your salary raise.