Hey,
I applied to SMP, but in the end, decided not to do it. I ended up doing a masters program at UMDNJ (cheaper, state school, flexible program) since I didn't just want to take classes. I'm doing a thesis right now and am valuing the extra, independent research.
However, my SPECIFIC case was that I did extremely well my last two years and mediocre (bunch of B's) during my first two years. Taking this into account, along with the fact that I got a couple A's in tough courses at Columbia (I worked there after graduating college, so tuition was free), I thought that it was more important for me to just do a little better on the verbal section of my MCAT. That apparently was enough. I took classes here at UMDNJ for my first semester and sent in my first semester grades as updates to schools, but by December, I already had 5 interviews, so the point is - these extra courses didn't really help or anything.
If you did extremely well in your last two years, then maybe doing a different masters program (a more traditional one - with a thesis) would be more beneficial since you're not "just taking classes" and doing a thesis as well - which could lead to publication. This of course, only applies if you're interested in research. If not, then you could look into public health programs (but I think most of these require 2 years). I'm finishing my program in a year and I'm sure there are other masters (aside from SMP) that can be completed in 1 year. Just keep in mind that if you do SMP, it should be because your grades are a little low (you know, like a 3.0-3.2) and you need a boost. If you have a 3.3 and don't really have a strong upward trend, then I say go for it.
If you decide on it, adcoms know it's a tough program and at the very least, it shows that you're dead serious about going to med school. If you don't do it, then I think you'll still have a chance with a 28, 3.3 (although "very borderline")...just apply to 20 schools, like I did! The third, alternate choice is to do the "traditional" masters program, like I mentioned above - the advantage is that 1) you can still take classes, although they won't be med school courses, 2) adcoms will still respect it, 3) you get extra research experience, so in case you get in somewhere early on, you won't feel like spending money on the SMP was a waste of your money. If you want to start fall 2005, you would just need to research programs that'll allow you to finish or leave in a year - I bet state schools would allow this - if you're around new york and don't mind snow, roswell park has a nice program. Anyway, good luck with everything and I hope this has helped. I was in your position one year ago...stressing to death, but after you get in and you know it's what you want - it's a great feeling. Good luck!