www.wikipedia.org: Rather than a generic focus of education, Nurse Practitioners are able to specialize in an area of study they desire (e.g. Pediatrics, Family Practice, Adult, Geriatric, etc.), and provide care within the scope of their expertise. As well, Nurse practitioners in certain states can be “psychiatric clinicians” and perform similar practice (though at a different level) as a psychiatrist would.
Salary.com: Nurse Practitioner salary (25th-75th percentile) is $67,166 – $78,497. Generalist physician salary (25th-75th%) is $115,260 – $152,715.
Wikipedia: According to numerous salary reports throughout the years, CRNAs remain the highest compensated of all nursing specialties. Their average reported annual salary range in 2006, reported by the AMGA Medical Group Compensation and Financial Survey, was $140,396. The mean annual salary for an anesthesiologist in the United States in 2006 was $184,340. 
What’s my point? Fair question. First, NP’s have the same scope of practice as any physician. This is clear from my first statement about NP’s specializing. Whatever specialty you want as a physician, there’s an NP that can do the same thing. “But surely not for surgery?!” is the cry of retort. Well I promise you that within the next 10 years, some politician is going to realize that “Hey! PA’s and Surgical Tech’s can pop out gallbladders just as well as a surgeon can!”
Also note the salary differences. Now I can’t find information regarding the various NP specialties, but compare the lowest specialty to the most basic NP, the salaries are comparable, and the highest NP position to the highest (according to MSN.com) paid physician. When you do, you’ll note that physicians do, in fact, win. And NP’s must do 2 years of post bachelors work and one year of work experience (for a total of 3 years) compared to the 4 years post-undergrad for a physician. Big whoop. One year.
Well please note, the average med student graduates with around $200K in debt, while, according to Barry.edu (a school in FL that has both NP and PA programs) the PA program (the more expensive of the two) is $24,810.00 per year. This is roughly equivalent to medical school. However, you’re paying twice as much in med school because you go to school for twice as long. Also, one of the 3 requisite years for NP school is clinical experience. This is a paid job. RN’s make (again, 25th-75th%) $49,479 – $59,114. That means that if a med student and an NP were compared at the same time, 4 years post undergrad, the med student would be out $200,000 (roughly) and the NP would be out $521 (rounding to $25K/yr for both programs, and using the 25th percentile for RN’s). Add the interest on a med school loan, and that puts you at about $600,000 paid back (bc you pay back about 3x what you borrow, esp the financial geniuses that make up our MD population).
Now lets say that no matter what you do, you make $30,000/year more than your equivalent NP. You figure that after 30 years of practice (putting you at the nice comfortable retirement age of 66 for those of us that took the direct route) and you’re up $900K. Worth it, right? Well we haven’t incorporated malpractice insurance. Have you ever heard of anyone suing their NP? I sure as shit haven’t. Factor in 30 years of malpractice insurance bills, and I’ll promise you it brings you right back to even (not to mention that physicians’ salaries are trending down relative to inflation while all nursing salaries are trending up). Couple that with the hours worked by an NP relative to an M.D. and the paperwork/legal hassles handled by an MD that aren’t worried about by NP’s, and the conclusion is obvious.
Do the same thing for the same amount of money, and have a better quality of life. Become an NP.