I once contributed to a localized version of SO whose licence was not open. The startup backing it eventually shutdown and the site disappeared. All time invested in those answers is now irrevocably lost.
Non-open content licence is exactly what made me stop contributing to sites such as Wikimapia and start contributing to OpenStreetMap instead.
Once you get burned a few times, you learn it's better to have to put up with a few clone sites than risk losing all the data, or having to pay to read what you wrote yourself a few months ago.
Thanks for the answer. I just want to ask one more question. Don't you think StackOverflow is already too large to disappear suddenly like those startups you mentioned, and smart enough to NOT go the way of ExpertsExchange? (I think the founder explicitly mentioned StackOverflow wanted to be an anti ExpertsExchange when they launched. Also I don't think the company would be stupid enough to alienate their users which will lead to demise regardless of how much content they already have)
Non-open content licence is exactly what made me stop contributing to sites such as Wikimapia and start contributing to OpenStreetMap instead.
Once you get burned a few times, you learn it's better to have to put up with a few clone sites than risk losing all the data, or having to pay to read what you wrote yourself a few months ago.