In reply to lex:
If you want light waterproof boots then really you are going to be getting something with a membrane. All the membranes will eventually fail, even more so on a light flexible boot. If it's a good leather outer you can mitigate somewhat gor the failure by waxing them heavily but this isn't a very light option and on light boots you're more likely to have mesh panels.
I'd say goretex is more robust but slightly less breathable than E vent. But most apparent failures of E vent I've had have been due to membrane contamination with skin oils, something that wouldn't be such a problem if you always wear socks.
People say about the breathability of leather but I'm not convinced any material is going to be very breathable once you cover it in wax as you are supposed to.