No it wasn't; I own an iPhone 3G and it stalls and stutters doing anything. It's consistently done that for the entirety of its service. My wife bought the 3GS and _that_ was when we saw much of the UI lag go away.

I moved on to Android and own a Galaxy S - there's virtually no UI stutter at all, I only see delays on shutting some programs or launching a few apps. My wife recently bought a 4S and it's very smooth, but don't tell me that iOS has always been this smooth because you're looking back with rose-colored glasses.