On Stack Overflow, comments like "let me google that for you" are banned. What is the policy on CS? Before that I was thinking to close them all, but right now, I think the policy on SO is better. As long as a question is on topic (there is no duplicate of that question, well written, has some audience in CS, ...), we shouldn't close the question and we shouldn't leave LMGTFY link as a comment. But I think is better to elaborate it here.
LMGTFY comments are almost always rude. Don't hesitate to flag them as such.
Banning them by automatic filtering isn't very effective: it only leads to people using other similar sites or link shorteners.
Politely encouraging askers to search for an answer is of course perfectly fine. But you should point people towards reliable reference materials rather than to Google. It isn't always easy to figure out which search engine results are applicable, and even more difficult to figure out which ones are reliable. Also remember that all search engine results fluctuate over time and that Google search results depend on your language settings, on your search history, on your location, and other factors.
Not spending 5 min to do a Google search before asking others for help is also rude. Of course there are cases where LMGTFY is misused but often it is the proper answer. It also teaches the person how to find answers himself, i.e. Google.
An LMGTFY comment does not forbid others from posting detailed answers or comments directly linking to a page with the answer.
Moreover, I think there are situations that an LMGTFY is a the proper answer, e.g. when the answer in clearly given in a Wikipedia article and the article is the first result when you Google for the obvious thing. Personalization of the results is unlikely to have an effect on such cases. The results might change over time, but so is almost any page on the web, that is not an argument for not linking to them. A question with just LMGTFY answer should be eventually deleted so there is even less issue with the long time reliability of the link.