1) the "gee whiz" temporary flash-in-the-pan bump of how well it demos, powered by every early adopter trying it once.
2) the "this is useful" compounding curve powered by word of mouth.
The two curves are different and distinct.
Things that demo well but are otherwise not useful have the first curve without the second.
Things that demo poorly but have an inherent network effect of quality have the second curve but not the first.
Some new products have both, like Google Maps did right when it was first launched.
It's easy to confuse the bump of the gee-whiz for the hill of quality.