Actually, I've had domains I've bought that were NOT parked picked up by the search engines. They were two variations of my name; not likely to be been owned before or expired. I was planning on pointing them to my personal site, but forgot about it, and lo and behold came across one of them in the SERPS one day; when I checked, the other one was there too. Another domain I bought, a .org, showed up as a #2 SERP under the .com without a site or parking or anything. Don't ask me.