I ordered a 32GB Black. I currently have a 16GB 3G, that's right 3G. In the 4 years, including all of the music and all the great pictures that my daughters took (for example some of the floor, or my trucks dashboard and some of their feet), I still had only used about 60% of the memeory.
However, my other considerations were iP5 takes 8MP pics (take up more space obviously) and will probably use it to take some video. So I thought, 32GB should be more than enough, and could probably get by with 16 if you managed memory more. Plus, there's iCloud and I probably only really need about half of the music, so i could remove the other half, so... that's my delusional reasoning.