An update for anyone following this: I managed to get Leopard installed on the SSD. It ran well to begin with, then the performance was terrible (videos and apps were stuttering and freezing) and now it seems to be quite snappy again. I don't know whether to persevere with it or ask for a refund. I've posted on the OCZ support forum to get their opinion anyway.
The 64gb capacity actually boils down to 56gb which is more dubious than the 'acceptable' losses you come to expect from hard drive marketing. I've noticed that the newer model ones are sold as 60gb which is much more honest, though it doesn't help V1 buyers like me very much.
I lubed up the fan bearings and that's eliminated the squeaking, though I'm now stuck with a more consistent, loud whooshing/spinning noise. Nothing out of the ordinary for the average PC, but a long way off the near-silent claims made by Apple.
It's probably actually back to normal, except now I'm using Fan Control to keep the CPU at a safe temperature (something Apple doesn't seem interested in doing by default) the fan noise is much more noticeable.
I raised the Mini off my desk slightly using a blob of Blu-tac in each corner. I'm not really sure if that's helped to reduce the temperature or not. While idling and with the lid off, the CPU is reading 62c while the fan spins at 1300 rpm.