When the iPhone 4 launched, I was a bit underwhelmed (lolwut?) so I chose to try an Android device. I bought a Samsung Galaxy S.
I was immediately disappointed. It was a lot of tiny things that bothered me, for example the gallery, it would take time to load the thumbnails - on my 3GS it was instant on my 3000 picture gallery.
The way the scroll worked - it didn't have the natural momentum feel of the iPhone, you made a small flick and the page would jump like crazy and keeeeeeeep going.

I'm surprised that only Apple got this right. I saw the Windows 8 presentation, and the same stupid issue, the scroll speed is HUUUUGE.
The pinch-to-zoom was awful as well, if you made a very very small pinch to zoom it wouldn't register like on the iPhone, it had like a lower-limit and if you surpassed it, it would register, same for the scroll. And the scroll speed really makes reading a web-page a nightmare.
Those days they kept touting benchmarks numbers and all that, but the phone felt so sluggish, even compared to my 3GS (I don't even know about iPhone 4). I kept looking for a fix, and I was amazed that all the owners would tweak and install all kinds of firmwares/roms etc etc... root your device, one click lagfix, new rom, new launcher (because Samsung's kind of sucks), task killers (are you kidding me?).
To keep an Android in working order seemed like a full-time job. Hell I work less at my office, and I get paid for it pretty good
So I switched back to iPhone. But to the 3GS, because I used my upgrade on the SGS (i have 1 year contract over here).
So I will no longer be fooled by the Android hype, there is A LOOOOOOT of dirt swept under the carpet, trust me. And all the little inconveniences will drive you mad if you used an iPhone for a few months before.