Pretty good, you would be surprised. I've always been of the opinion that even the iPhone jailbreak community is better organized than anyone who hasn't tried it in person realizes. Via tweaks like DreamBoard you can customize anything and everything. Even total overhauls like turning it into an Android style or WP8 style device. It's pretty remarkable.
It's worth getting ahold of a 4S and jailbreaking to check it out firsthand if possible. The impression I get from Android users is that they feel iOS is completely impossible to customize in any real way. IMO installing total overhauls is actually easier assuming you're past the jailbreak process, which also tends to be simpler than rooting (although obviously that depends on the specific Android device you're trying to root).