The only statistically significant data I've seen about organic traffic changes following Google Instant shows an increase in video click-throughs. That's all.
The long-tail/short-tail comparison studies show only minor differences in some verticals only, and those differences are not always in the same direction from test to test! Some studies say long tail searches went up a tad, others say they went down a smidge.
I conclude that the world as we know it has not ended. It's certain that my smaller business clients noticed nothing.