Compared to my previous phone, the G1, the Desire seems to just keep going.
My G1 towards the end was only lasting hours and spent most of the time either charging by the bed, in the car or via the laptop. That said my wifes G1 seems far more gentle on it's battery, we even swapped batteries in an attempt to prelong my battery life but mine stayed as hours, and my wifes as a day or so.
The key issue appears to be what your running on your phone, even switching GPS and WiFi off my not save too much of your battery if poorly written applications drain it instead.
As said at the start, my experience of the Desire's battery life is far more impressive, and that is without froyo, who knows we might see the day or so of operation stretch into days, and possibly threaten a week?