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I've done this for a few years with some entire websites that weren't open to the public yet. Seems to work ok for the most part, and sense the data DOES exist and is going to exist by the time the lathargic search engines update, I don't see a problem with it. In fact, it helps the engines by giving surfers timely info about upcoming features and news.
For example, I have a friend who has "preloaded" a serious site full of info about a product to be released in late june. He's submitted to most of the major engines and kept the data hidden via cloaking. When the product goes live, he'll uncloak the site. Searchers will instantly find the data they are after when the "buzz is hot" about the product.
I understand the concept that you are speaking about, and I can see why this would bring good, or quicker, results.
My question is this: If you are still developing the site, then what are you going to give the SE's to feed on?
It still works, it just takes longer, which I suppose is even more reason to do it now, cuts down on the long lag times.