Something I was doing the other day - working with .htaccess files - made me wonder where it would belong if I needed help - Stack Overflow or Server Fault. There might be some topics that fall in the middle, where they are of interest to programmers/developers, but it tends to be more on the IT side of the fence (database configurations are another good example).
So how should I go about deciding where to post a question? Should it be possible for me to use one site and cross-post (and gaining the rep on each side for that side's account, or for one to be forced into community wiki)?