Following bunnspecial's recommendation of an mSATA SSD and 2.5" IDE enclosure, I bought one to try out in my 867 MHz 12" PowerBook G4. Up until now it's been running with the 60GB drive the machine shipped with in 2003, which has been dreadfully slow (too slow to run Leopard well, even with the full 1.12GB memory). The SSD gave a noticeable increase in performance and made Leopard actually run quite well. Of course this is hardly a fast machine (unlike my PowerMac G4) but at least it runs well enough to use again - especially coupled with Erik's excellent TenFourFox tweaks. The laptop also runs a lot cooler, I very rarely hear the fan come on now whereas before it would be on regularly. The fact that it's silent is really nice. With the decreasing availability of 2.5" IDE hard drives and the ever falling prices of SSDs, this is definitely the way to go for anybody looking to replace or upgrade their PowerBook's hard drive. One other thing - as OS X Leopard lacks any sort of TRIM functionality - are there any things I should do to maximise the lifespan of the SSD? In case anybody wants to know, this is the mSATA enclosure that I used.