Sometimes on SO, some people ask questions that could be simply answered by doing a quick google search and finding a blog entry for example. What your opinion on answering such questions by posting links instead of answering from scratch ?
People who answer questions are using their time as well. It can be convenient for someone to post a link, especially if it is a lengthy tutorial or a content resource. If someone wanted information on how the syntax for a certain kind of formula program, it saves time to link an online resource rather than trying to copy over an entire set of webpages. As well, these kinds of resources tend to have the advantage of better formatting than what you can accomplish with answers.
That said, if the information that is needed from the link is minimal (i.e. the answer is found within the link, rather than the answer is the link), then it is much more helpful to include a citation and/or summary of the relevant info.
It's always better to try and add some of your own content, be it to explain, clarify, or simply narrow the information of the link to apply to the target. This is especially the case if the link is more of an "extra reading". Just like linking saves the answerer time, explaining links will save the question asker time.
I try to always include at least a relevant snippet if I post an external link to something because links can / will break over time. When that happens the usefulness of the answer is lost.
Of course, always attribute them as appropriate.
I have no problem with people providing a link to the source they used to find an answer, as long as they summarize the link's contents as well. If that link suddenly breaks one day, the answer should be sufficient to stand alone and help people who read it in the future. I've had entirely too many Google searches link me to forums that say "Yes, [the exact problem I'm having] is easily fixed! Just go here to find out how:" and discovered the link is broken because it went to somebody's blog that they maintained for 20 minutes and abandoned
Jon Skeet has written a guide called, Answering technical questions helpfully which answers your question very well.