As the previous agent mentioned below, I also haven't seen BMRs (below market rate ) affect condos value anywhere in San Francisco. Also, just for you to have an idea, I checked some data from last year (May 20013), and the median sales price for condos in SF were $825,500 compare to $952,500 - May 2014 (Source: San Francisco Association of Realtors). I hope this was helpful. Take care!
BMR (below market rate) apartments are required by the city in new buildings. In my experience in the city and as an agent, I haven't seen these units impact the market rate units at all, nor do I think they in any way lead to increased crime rates.
I'd be happy to help with your condo hunt if you need it, and don't hesitate to ask if you have any more questions.