This thread has been rather helpful, I need to change the front lock as it's starting to get hard to put a key in at times (not just the one key but any of the ones for it), so I was looking at keyed alike and replacing the back door one at the same time, and given the fun and games we've had recently on my street I'm going to go with the Avocet ABS ones.
It's now looking like I'll end up replacing the front, back, patio and garage door locks with a set of keyed alike ones, and take my house/car keys from 5 to 2.