I have used a pretty wide range of smartphones - from WinMo phones to Sony Ericssons to iphones - and I have never had a phone lose more than a couple of percent of battery life overnight.
I definitely dont think it is a 'smartphone problem.'
If that's the case, then perhaps my Hero was running something in the background.
So I've been messing around with Qik and Bambusters (live broadcast over web) for about 40 minutes and it drained 20% of the battery.