Does the HR usually takes care of these negotiations or the hiring manager? If it depends on the company, then the one I am talking about is a multi-national company with over 13 thousand employees in the US alone.
Also, when asked about your expectations, do you give a firm number or a range?
Re: Salary Negotiations
Depends on our level. If you are coming in at an officer or executive managment or senior management level then you negotiate with the principals of the company. If you are coming in with middle managment then you do it with Senior managers. If you are coming in as lower management then HR will be your conduit.
Give a range that drives mean over the listed salary or market comp.
Re: Salary Negotiations
In this perticular case there are three people I am in contact with. The HR person, the boss who I will be working under and his boss. I send an email to one, but the other replies as it gets forwarded to him. I reply to him and his boss replies back. I think they haven’t quite figured out who is in charge yet. 
Anyway, without discussing it with me they came up with a number. Its good but I don’t feel motivated to leave my current job for just for that. Though the bonus number is big but that doesn’t depend on my achievements alone - the company has to be making some serious money too.
Re: Salary Negotiations
I think in that scenario you need to give tangible examples of why the number you have in mind is worth the risk they will take and vice versa. You are leaving your job you have had for X years, your promotional track, your salary increases, your benefits, responsibiities, challenges etc... build a business case why you deserve that pay. Confidence in yourself is worth atleast 20% premium on market rates.
Re: Salary Negotiations
In my experience at large organizations, it is best to only mention what you are currently making (maybe add a bit, if too low) and tell them that you are nogotiable. When I talk about money I always talk about the guaranteed salary and bonuses and not the "IF" items.
HR provides guideline to the manager as to the range of salary that is allowed for the position/experience in that particular company. Usually someone within the organization is allowed to override the guidelines and offer more compensation.
As far as salary is concerned, it is ultimately the manager's decision. In some cases the manager may have to get his managers approval when the amount is above budget. Typicaly HR only provides guidelines, logistical help and acts as a middle person. In other words you negotiate with the HR, but the manager is the real decision maker.
If you are in the market and MIcrosoft interests you, send me a PM, I will be glad to lend a hand. As you can tell I work for Microsft and no, I'm not in HR or recruiting :)
Hope this helps.