As far as I know, SO does not own a patent covering a "method of scoring answers" or "method of calculating value of user submitted content" , or anything of the sort. This is one of the biggest reasons why the term intellectual property is so dangerous, its ambiguous.
When implementing some kind of new software, you should have the diligence to ask:
- Am I violating another's copyright?
- Am I violating another's patent(s)?
- Am I violating another's trademark ?
Copyright pertains to written works (which could later be performed in some way, i.e. by acting them out or recording as a song). Software is a written work. Unless you have the actual source code to SO itself, you are in no danger of violating copyright.
SO (afaik) does not hold a patent on any part of the user process.
Don't call your site stackoverflows or serverfaults, even just out of being a good neighbor. I'm not sure if either name is trade marked, If they got a trade mark for Stack Overflow, they had a really good lawyer.
Its worth taking some time to understand the differences between the three topics that are covered by the term intellectual property.