Thanks for all the thoughts all - I should state I'm not using them for commuting, I still have the eggbeaters which are the best clipless system ever for that. (ducks)
Just a bit surprised how quickly they wore out, but from what you've all been saying I have perhaps been abusing them a fair bit. Good to know replacements can be had for £10 rather than the £20 I'd seen, and I'll definitely be investing in some covers.
I could also do with learning to track stand.