Personally, I don't know how anyone who texts or emails a lot can live with iOS' keyboard. It often misses keys (as in unregistered taps), autocorrection is often off, there's no suggestion bar, and no long pressing for secondary keys, etc. The keyboard is so poor that it's given rise to numerous websites that make fun of ridiculous and unintended autocorrections.
ICS' keyboard is now leagues ahead of iOS'. The autocorrection is phenomenal, it's more responsive (hardly ever misses taps), and little features like auto-separating typos (e.g. accidentally hitting the 'b' button instead of the spacebar when typing two words: "hibthere" will auto correct to "hi there") just makes the keyboard feel smarter and more user friendly.
There are things I miss about my iPhone, but as someone who emails and texts a lot, the switch to ICS was logical. I'm keeping a keen eye on iOS 6, and hoping improvements will finally be made to the keyboard.
iOS keyboard does the auto-separate thing you mentioned. Mine does it all the time, in fact.
However, I do miss the longpress from Android, for quick ? and ! typing, as well as numbers. But on my iPhone, I've found that you can press the "123" key, which instantly changes the keyboard to numbers and charactes, then you just drag to your desired key and release. It will type whatever number/character you released from, and automatically switch back to the letters layout. It can actually be faster than Android's longpress, since it's just a quick swipe with no waiting.