iPhone
Almost 3 years ago, I made a huge leap over to the iPhone, and I've honestly never looked back. I'm still using the exact same phone even now, running the latest OS. What first turned my head about it was its simplicity. There was no misinterpreting what it was showing you. After a while, though, I became apathetic about one thing-- the GUI. Namely, the lack of customization of it. Unfortunately, Apple doesn't want us to have that power (yet). Fortunately, other (awesome) people do. Anyway... I started creating my own themes immediately after jailbreaking. Call it a compulsion.

Before anyone asks, yes, I've done more than one theme. Sadly, I'd been doing my most recent sets around a really amazing app called LockInfo, which places weather, full calendar and clock, system notifications (SMS, mail, missed calls, etc.) right on the lock screen. And in interactive style, no less. The best part is that it has always been easy to override its default settings with some basic Webkit scripting (that's more or less HTML/CSS/JS). The bad news is that LockInfo is now a paid app whereas it had been free before, and as a result, I'm having to segregate and re-bundle a lot of my theme components, and this takes time. I will upload additional themes as I complete them. If I had all the time in the world, I'd do nothing but this stuff, but alas, other things need tending to as well.