Sorry for the late reply,
Hardware wise, it will last a good few years as it's designed to take the knocks & be dust & waterproof. I wouldn't go chucking it in a pool but it's safe to rinse under a tap.
Software it goes up to 2.2 but if you look on XDA devs site they are still on it. I am on 4.1.1 (custom). There's tonnes of custom roms on there to choose from.
Most people root with superoneclick, install recovery then flash custom roms with that. Defy is kinda 'dumbed down' to 800mhz but easily does 1000, some people have 1200. Imo rooting it is about customizing the settings so yes you can overclock, but can also make battery savings.
It's a bit of a cult phone so moto bought a few newer models out based on it (before google bought them out).
