My first 16GB Phone was the Nokia N900 and found that 16GB was just too tight, so for my iPhone 4, I went with 32GB, don't regret it a single bit, and with my next iPhone 5, I have already pre-order the 32GB one.
My wife has a 16 and I have 32 gb iPhone 4. I found the 16gb to be little bit of a compromise but have not found a way to exhaust the 32 so I would say that is plenty for the vast majority of people.
I am an IT guy though so I have gone and ordered a 64gb iPhone 5 because no one has ever said 'gee I really wish that I had less storage on this thing'
I'm getting the 16gig version. I didn't get anywhere near filling up my 16gig iPhone 4 so don't really need to shell out the extra cash for the 32gig iPhone 5.
64GB white and factory unlocked - for me its factory unlocked or no iphone at all and 64GB I use up so much space and dont like to rely on itunes match. what ever the max space is that is what I will always buy
I've had a 32Gb iP4 for 2 years and early on I had all my CD collection (approx 350) stored on the phone which took up around 20Gb if I remember correct. However for the last year I have reduced the music down to about 10 albums so that I can fit all my apps on and always strugle to maintain 1Gb free if Im lucky. Remember its not necessarily apps themselves that take a lot of storage space, for me its the data I store in the apps. i.e. In my photo album I have around 5Gb, in PDFMaps I have around 7Gb. In FileExplorer I have around 4Gb of pdf docs. And then in I must have several Gb in Kindle, Zinrio mags and Kobo books. So it all depends on what your are using your phone for other than just a phone.
For me I would like my iPhone to have around 500Gb. I think I will have to wait a while yet. In the meantime I will be soon getting a 64Gb iP5 and continue to manage what I store.