There has been a recent discussion on the AskUbuntu StackExchange site about including the word "Ubuntu" in questions to provide better "googleablility". While I assume this is wrong, I don't know enough about Search Crawlers and the StackExchange platform to confirm this.
"Ubuntu" is already included in every page title ("Question title - Ubuntu - Stack Exchange") plus numerous times on the page. Any search engine that can't associate Ask Ubuntu posts with Ubuntu isn't worth worrying about.
Make question titles useful for real people first, and search engines will pick up on real people finding the site useful — which is the basis of Google's success. Including "for Ubuntu" in every question title would get really tiring and lead to less user participation (through confusion and frustration) if enforced — much more disastrous than a loss in SEO, even if that exists.
Not sure about duplicity of a keyword weight in SEO.
Order and quantity matters, but I think the right spot for this question regards about long tail, and this demands a behavioral study about search (how people do searches?).
By my experience, people tends to search for keywords, and change the keywords order.
From you comment on John Conde ("What native games are available? - Ubuntu - Stack Exchange") I can foresee the following:
users usually will search for - [native games ubuntu] - [ubuntu native games] - [ubuntu native games available] - [native games available ubuntu]
And other variants. So,
What native games are available? - Ubuntu - Stack Exchange or What native games are available on Ubuntu? - Ubuntu - Stack Exchange
Will most likely match for any case of search listed above, making not at all or almost nothing difference for biggest part of searches, making no sense to duplicate. Only a really few users will search for:
These cases are the long tail where changing titles can probably make a difference. Also, consider users would also search for:
And a lot of options that will not perform a really good match. Also note that these not so good matches list is much more frequent (more users performs them) than long tail ones.
Closing thoughts I don't see a point to duplicate the keyword in title for this case considering users behavior and long tail.
Having keywords on your question, which is used in the page title, is very good for SEO and for your users (which is no coincidence). The title of the page tells whomever is viewing it what the page is about. That includes the search engines. Since the title of the page is essentially a very short description of what the page is about it makes sense that having keywords in it would weigh heavily in determining a page's relevance for a search query. It's also good for users when they bookmark a page as the title is the default label the bookmark is given. When they go back to the bookmark having keywords like "Ubuntu" help them recognize what that bookmark's contents is. You can't assume they remember it is specifically for Ubuntu weeks, months, or years later.