And from that same page, there was this link to the additional Medicare tax:

http://www.irs.gov/Businesses/Small-Businesses-&-Self-Em...

This one is more convoluted. If you are married and filing jointly, the income threshold is $250K. So, basically, everything the two of you pull in over $250K gets slapped with a 0.9% Medicare tax. But your employer only collects the tax on individuals once they surpass $200K which is the limit for single filers. Well, if you and your spouse make $150K each, your employers take nothing extra because individually you are both below $200K. Here's the rub. At $150K each, you must make estimated tax payments using a W-4. In this example, the combined income totals $300K, or $50K subject to this tax. The examples provided on the website do not address what happens if the additional estimated payments are not made. What happens if you make estimated payments and it wasn't enough? Will you just write a check at the end of the year like you do with the Federal income tax return or will they just take more out of your salary over the following year? This is not addressed and I can see this happening A LOT because many people will not get to the $250K level jointly until the very last couple of weeks of the year, when they get paid BONUSES that they have no way of being able to estimate as they vary from one year to the next.