Although Geth has always worked on the RPI, we haven't put much effort into optimizing for such low end devices. During the Olympic testnet I did make Geth syncable on the RPI1, but there have been quite massive modifications and it wasn't a priority to keep this platform operationally feasible.
We're currently in the midst of releasing Geth 1.4.6, which will mostly be a networking fix to allow lower end connectivity peers to stably sync, but after this, work will commence on various database optimizations to make lower end devices feasible again. I can't say how low we'll manage to go, but I would definitely like to see RPI2 at least capable of running a full node.