"A day" is subjective.
"A day" to me means 16+ hours. Long enough to wake up, take my phone off the charger, go to work for a full 10 hour day, hit up a bar/store after work, and hit my bed that evening with enough juice to not need a charge. I want to be able to use my phone moderately during that time. Every other smart phone I have used makes it through that usage pattern.
"A day" for the Droid Incredible is ... take it off the charger, dead by the time I leave work, requires a charge somewhere during the day to make it through any manageable period of the evening. Additionally, I have to severely limit my usage of the phone, disable a significant amount of features, turn down my screen, and for the most part kill any background app that would use any amount of CPU.
However, the issue isn't the phone. The reality is the battery is slightly undersized for the cdma/cpu combo on this phone. To be on par with most other touch screen smart phones they needed to include a larger battery out-of-the-box. Fortunately, we can purchase one...