Technical Sales Director at Symantec Corp
certain careers are very dependent on education and certification, such as engineering, medical, etc, so if you plan to enter into those fields, picking a major is important. I would also add that the math and science careers are looking more and more for people with advanced degrees, so your undergraduate major is important.
The more social sciences like political science, sociology,history, criminology, pre-law, etc. are a little less reliant on specific degrees which is why liberal arts colleges require you to take a broad range of classes in various disciplines. Advanced degrees are also available in these areas but there is a little more flexibility in switching between disciplines than in say engineering or medicine.
All this being said, the most important thing is to do well in whatever field you choose and to get involved in extracurricular activities related to the work you would like to get into. Employers look for people who can set goals and achieve them and college is one of the first chances for young adults to demonstrate their ability to handle the rigor of completing tasks and assignments on time.
So don't fret if you choose a major and decide to switch, but try to do your best in all of your studies to demonstrate that while you are unsure what you want to do, you have the ability to do well in whatever you do.