I have always kept my 16GB full. The 32GB, not so much. However, this will have a larger megapixel camera and HD recording, and books, so your mileage may vary.
Most of us will have at least 1.5GB for a navigation app, and some of the cool games are getting into the hundreds of megabytes.
If you have the grandfathered unlimited data plan, you could get away with streaming music and videos from SimplifyMedia (if you still have that), the multitude of radio apps, and SlingPlayer and Air Video, and therefore depend less on filling up the iPhone with music and videos all the time.
Most of us will have at least 1.5GB for a navigation app, and some of the cool games are getting into the hundreds of megabytes.
If you have the grandfathered unlimited data plan, you could get away with streaming music and videos from SimplifyMedia (if you still have that), the multitude of radio apps, and SlingPlayer and Air Video, and therefore depend less on filling up the iPhone with music and videos all the time.