I think that it is entirely normal to take two years off. It is so normal, in fact, that two years off barely even makes you a "non-traditional." It's practically a standard route to medical school these days. Some thoughts:
1) I have seen many of my friends who took time off end up with a much more solid application to medical schools. I'm talking about people who had lackluster academics earlier on in college who that would probably land them a spot at a top 50-30 school suddenly become UCSF and Hopkins material, and so on, because they were able to boost their GPAs, have time to study for the MCAT, and participate in a few more extracurriculars in that time. Senior year is when many students' GPAs go up because they're finally in senior seminar courses, which aren't always graded on a curve. Senior year is also a time when students have more opportunities to take electives instead of weeder classes, and so on. If you apply during your senior year, obviously these classes aren't factored into your GPA, so you don't have that boost without a gap year.
Same deal with leadership positions-- many students finally land TA positions and leadership positions only in their senior year. While it's okay to write that you have been elected leader at the time of your application, you'll make a stronger case for yourself if you can actually write about what you DID in said leadership positions, which you can really only do if you take a gap year. Research-wise (if you are interested in a research-heavy school), taking a gap year also allows more time for publications to actually get, well, published. The revision process takes forever and it really is a challenge for many students to have publications without taking a gap year or two.
The majority of my friends who took gap years worked in a lab for two years (it seemed like everybody on the interview trail was doing "research in Boston"); some did research at a medical school they were interested in attending to get a better feel for the city and institution. However, I would suggest doing something non-medicine related for reasons I'll talk about below:
2) Cons to taking time off: well, it's two years of your life in your twenties. I see people make the argument that it's nice to have the time off to "relax," but if you already know that medical school is your goal, in some sense, "taking time off" is just postponing things. In other words, it's one thing if you want to take two years off to figure out if you actually want to go to med school in the first place, and another if you are taking time off to bolster your application. People in general don't *actually* want to work in a lab for two years (unless they want to do MD/PhD). This is why I would suggest doing something non-medicine related during your gap year, and then continuing some clinical activities to demonstrate continued interest in medicine instead if you are to take time off. It will look the same on your app as long as you can talk about it intelligently and maybe tie it back in to certain aspects of healthcare. The only difference I can really think of is that certain labs in Boston (at the Harvard-affiliated hospitals) have connections to top-tier medical schools, so working there could possibly help your application as well. But uniqueness also counts a lot in the med school application process, so doing something fun (one person I know went to cooking school) won't hurt either.
Are the two years off worth it? Only you can tell. To some, med school is med school, and if your goal is to become a doctor, then maybe going straight through would be the best option for you. Medical training is a really long road, and two years, while not a terribly long time, is still substantial.
On the other hand, if you want to go into academics and try to get into the most prestigious medical school possible, then taking time off might not be a bad idea.
Also, if you have student loans and aren't enrolled as a student, your loans will go into repayment during your gap years. So think about that.
