Facebook was much better for this in the old days when they had a concept of a "restricted profile". You can still do something like it with groups, but it's much more administrative overhead, I wonder how many people bother.
It's not that bad... keep a "safe list". Every time you add a friend either add them to the safe list or don't - it's right there on the add friend dialog. The "safe list" gets to see everything, the other list gets to see nothing but the basic info on the profile. This way you can friend anyone without offending them a rejection but at the same time keep professional contacts at arms reach.