A Google-fu answer is perfectly acceptable if it is correct (and, coming from SO, if it also contains the relevant information instead of just a link). If the poster was able to find it on Google (or if they would have hit Google first) then they would not have asked the question in the first place. Sometimes people don't even know what to search for and by pointing them to a Google result you give them relevant keywords and a starting point that they didn't have before. In any case, they asked because they did not know the answer and either did not know how to find it or came to an SX site first -- a Google-powered answer helps them (and potentially others) and that is the real goal.
As for answering a question when you have no real knowledge of it; I fully support this as long as you can come up with a correct answer. I do this all the time. When I have free time, I go to SO and start researching and providing answers to questions that I did not know the answer to. For me, this is how I learn best. Over the years I've learned an incredible amount by simply finding the answers to unanswered posts on various forums (on some I titled myself "Google Relay Server") - I feel it keeps me from getting stuck in ruts sticking to what I know. At the same time, it has the added feel-good bonus of contributing a little bit of real knowledge to the internet, and for every other person in a bind who finds it as an answer to their problem, it is worth it. I know I always appreciate finding correct answers to my questions.
In my opinion, the true goal of sites like this isn't to show off or to grab "reputation points"; it is to contribute to the internet as a source of information and collection of human knowledge so that others can continue from where we left off and find information without having to go through the pain of re-deriving it for themselves, and I fully support anything that contributes to that, including Google-powered answers.