Step 1 is a very important exam no matter what field of medicine you want to go into or how competitive that field is or isn't. The exam probably counts much much more than it should, but many residency program directors feel that it is the only national "standardized" tool they have to compare applicants from different medical schools. While Step 1 is by no means the only thing people look at on a residency application (extracurriculars go a very long way), doing well on the exam only opens doors for you, and doing poorly may prohibit you from going into to the most competitive fields. 93% of people pass the exam on their first attempt, which means that a few people will fail the exam... it's not the end of the world. But if you stumble on the exam and want to go into a competitive field, it is important to be well rounded and have an area (volunteer, class rank, research, leadership, etc...) that compensates. While there certaintly is no magic number, to be a candidate for almost any field, above 230 should suffice... of course for the most competitive fields (ie. optho) the higher the better, but a 230 supplemented by a strong personal statement, letters, applicaton, ect. should be just fine. Of course, for most primary care fields, near national average (215ish) will be just fine (even at top programs provided your application is well-rounded).
While occasionally some really top programs in the most competitive fields use Step 1 as a screen (ie. a certain radiology program may only review applications of students with > 225), Step 1 is only a PART of your application. Programs also review your Dean's Letter (aka. MSPE), application (pretty much your resume -- work, awards, extracurriculars, research), personal statement, clerkship evals, letters of recommendation, and step 2 score; not to mention how important the interview is! I know some people that rocked Step 1, but had no other substance (no extracurricular involvement, no leadership activities...) to their application and therefore were not getting many interview offers.
Somewhere along the way, you have to ask yourself: Do you really want to go to a program that sees you only as a step 1 score that reflects one day out of your entire medical school career?? I certaintly didn't when I was applying last year.
In general, residency program directors value Step 2 MUCH more than Step 1 because, let's face it, how you do on Step 2 correlates with how strong your clinical knowledge base is while how well you on Step 1 simply correlates with how well you know the Krebs cycle (and in residency no one cares about that). The reason that Step 1 is such a big deal though is that very few people have a Step 2 score available by the time they apply to residency, and therefore Step 1 is the only standardized measuring stick these programs have to compare applicants.
Fellowship applications are variable.... some (very few) don't ask your Step scores at all while others want everything and the kitchen sink -- SAT (no joke), MCAT, Steps I - III, and residency in-training exam scores. Most do see all your Steps, with Step 3 counting more than Step 2 counting a lot more than Step 1.
I hope that this helps relieve any anxiety you may be having. Remember that there are always expections.... someone from my class failed Step 1 twice (thus had to sit out a year) and still matched in a good optho program whereas someone at the top of the class didn't match.
The bottom line is that there is no magic number. If you didn't do so hot on Step 1 though, and you want a strong residency program, then you better have something else in your application to compensate (and maybe even use part of your personal statement to explain why you did poorly). If you did great on Step 1, then it'll compensate for an area you may be weak in on your application (ie. leadership/extracurriculars or research) or enhance an excellent application).
Good luck!
