I think decent is a subjective term. Some people may be happy to get 8 hours use out of the standard battery while others would complain. And battery life is dependent on so many different factors that it's hard to say for certain what each person will get.
If you want more juice but don't want a thicker battery, wait for Seidio to come out with their batteries. They usually have one in the 1500-1750mA range that's the exact same size as the standard battery.