Picked up my S5 yesterday to replace my S0 as well. Very happy with the upgrade. Not ditching the S0 though, I'll keep it to wear when the S5 is on charge ( I put it on when I shower and take it off before bed once it's charged up), as well as any activities that may cause damage, such as mowing the lawn. Give it 6 months or so and I'll be less careful about looking after it, then the S0 might see full retirement.
Only thing I'm still waiting on, but not holding my breath on seeing, is ECG in Australia. Although it wasn't a deal breaker for me, I know some with heart issues that would like the feature, just for keeping an eye on things.