jrg,
Could you elaborate on what your research interests are? A lot of times, these research interests can span so many different specialties in psych; for example, I'm mainly interested in JDM and emotions, and there are professors that specialize in that within social, cognitive, I/O, organizational behavior, marketing, etc.
As far as applying to back-ups outside of I/O, I think it kind of depends on how your final profile shakes out. The reason I say this is (and just for your reference, I applied to 7 social psych PhD's and 7 marketing PhD's for fall 2011, so I've been forced to explore this a lot) that business schools often require more quantitative qualifications than psych programs -- like higher Q GRE scores, some math courses, stats, etc. So if you absolutely destroy the math part of the GRE, business schools might be a good back-up for you if you can find faculty that would match with your interests. If this is not the case, I think I would echo the sentiment of other people on this thread to say that you should probably stay away from social psych PhD programs as back-ups: Social psych is probably the most competitive field in psych outside of clinical, and often times, you could improve your chances if you applied to faculty in cognitive or developmental (you'd be surprised because a lot of times, faculty can be cross-listed in multiple fields and have very "social" specialties, even if they're not technically social psychologists).
If you'd like more info., PM me or ask away. I'm in the process of waiting right now, so I feel your pain lol. Good luck!