No, just no. There is no point to any of all this search technology and this accumulated knowledge if no one uses it.
Someone asking a question that is answered in the documentation or has been asked and answered over and over should be pointed at those sources. One of the most important skills anyone is going to learn in a technical position is finding answers to questions you have that have already been answered. The next important skill they have to learn is doing a little bit of your own research in understanding your problem.
This goes especially for places like StackOverflow which is not a discussion forum. It's value is diminished by asking and answering the same questions over and over.
EDIT: I'll mention the last part of the statement I quoted too, it's unfortunate the lumped the second half of the statement with the first.
> correct their grammar, or give your opinions about their choice of technology
Correcting grammar is not helpful in any way in this context. If you can't understand what they're getting at, ask for clarification. Nitpicking grammar is just being a dick.
Opinions about what they're using may have one very narrow use, if what they're using to do what they're trying to do is just so very wrong. And we're talking 'I'm trying to create a pure HTML page to run this Nuclear reactor' levels of wrong. Most of the time, you do need to keep it to yourself. Especially on sites like StackOverflow, which is not a discussion board.