Does quick software always leave the best impression on users? In many cases, yes of course: people hate when a slow computer gets in the way of what they want to do. But I wonder if an application that's too zippy can be perceived as cheap in some cases.
Analogy: Everybody loves low prices, but if you sell your product at a bargain (or give it away for free), its perceived value can suffer. People see a competitor who's charging more than you and assume their product is higher quality.
Compare:
* "It's free so I guess it's not worth much."
* "It takes no time to load so I guess it's not doing much."