On the stock battery, I can usually get a full day out of a charge with my regular use, which includes alot of texting, alot of facebook, and moderate amounts of web browsing, as well as the occasional phone call and youtube video. I also keep have a car charger in the car in case of emergency as well as a spare wall charger that I keep in my center console since when I travel my phone charger is usually one of those things I forget on my way out the door.
If I could get a larger battery that I could use the stock battery back with I would consider an upgrade. Ive also thought about the whole extra battery and charger route. I could never use a battery like the 3500mh though, mainly because when I sit my phone and my laptop on a flat surface, I perfer my phone to be the thinner of the 2. Id rather have to plug in for a few minutes in the car or whatever than have to deal with the extra bulk and weight in my pocket.