Vacation time is not free

In addition to math essentials, I recommend Penelope Trunk incorporate a few accounting essentials into her career. In her post http://blog.penelopetrunk.com/2005/01/08/math-essentials-for-your-career/ she states:

Extra Vacation time is free to the company

Extra vacation time is not free to the company. When an accountant pays an employee for time not worked an account is charged in the general ledger called vacation expense. Expense accounts are used, in most cases, to record costs. In addition to paying an employee for time not worked, the company may actually incur additional costs due to an employee’s extra vacation. The employee’s work still needs to be completed. He/she may need to work extra hours resulting in overtime pay to get his job done. Also, co-workers may work additional hours to cover for him in his absence. If his work is not completed there is always the potential for lost sales and lower productivity.

I understand the point of Penelope’s post is to get you thinking about benefits other than salary when negotiating your compensation package, but she is wrong about vacation time being free to the company and it isn't always that simple. She states in entirety:

Getting a Raise

Use numbers to negotiate your raise, too. When it comes to compensation, do your own research to present a rational, numbers-based explanation for why your salary is not in line with comparable salaries in your field. If your company won’t budge, figure out which non-financial perks will equal a financial perk. (Finally! A use for high school algebra!) For example, extra vacation time is free to the company and a laptop, after tax deductions, is very cheap for the company.

I am not saying don't ask for additional vacation, I have received additional vacation in lieu of a raise higher raise in past employment. After the 2001 downturn and as more companies switch to PTO plans, I believe extra vacation is not a benefit handed over easily. Other benefits that are more readily given to employees are payment for additional training if job related, especially if asked for during a profitable period. This shows initiative plus the company benefits from your increased knowledge. My company has given laptops, but only to employees that are not in the office on a daily basis or travel a lot. Another benefit I've seen given is to for the company to pay an employee’s high speed internet connection if they do a lot of work from home.

Don't be afraid to negotiate non-financial benefits, but do know your facts up front.