Google point too about Autocomplete affecting when people stop typing. I think whether or not the long tail still has opportunity will ultimately come down to the range of search suggestions Google offer in their Autocomplete drop-down list. If people come to accept Google’s search suggestions as finite, the number of creative / unique / ad hoc searches would steadily decline (already there is some evidence of this as I point out in an article on Google Instant I worte recently http://www.alanmitchell.com.au/discussion/the-laziness-of-google-instant )

If that is the case, I don’t think the long-tail is necessarily dead, but it is certainly limited to some extent by the comprehensiveness of Google’s search suggestions.

On the other hand, if people take a completely different approach to Google Instant altogether, and instead increase their demands for even more specific, detailed results, as you pointy out, then the long-tail could in fact grow.