I've noticed this a couple of times recently. There have been a number of steak questions, specifically Cooking steak on the grill, where I feel like the information has all been well trodden on the site, but I couldn't find an exact duplicate to close as. Closing with a "Read all the stuff with the Steak tag" doesn't seem like a great solution either.
A recent question, Getting better in the kitchen, about beginning to cook, was just closed by Aaronut. Again, I do not think this is an exact duplicate. The new question is really about getting to a point where one has the prerequisite knowledge and skills to be able to improvise in the kitchen, where as the question it duplicates is really about starting from square one. It's not a huge distinction, but it is one. There are also a whole bunch of questions linked in Aaronut's comment that also cover similar ground. This seems very similar to the steak example. I don't think it's an exact duplicate, but it covers similar ground and a lot of the information that could go in an answer has been covered somewhere else on the site. But is a question really a duplicate if the close reason includes a link to half a dozen questions?
So when does a question become a duplicate? Have we covered steak well enough that any new question should probably be closed as a duplicate and involve a link to 3 or 4 different questions? That doesn't seem particularly satisfying to me, but on the other hand neither does rehashing the same conversations over and over.
Some thoughts from the SO blog: Joel argues for closing (although he argues against it if there's a ton of extraneous info or a RTFM approach) and Jeff argues that it's probably ok, unless I'm missing something in their arguments after an admittedly light read.