The iPhone is designed not to easily upload files. Not only couldn’t Safari (iPhone’s native web browser) do generic file uploads to a generic web site, no iPhone web browser or app could do it. I don’t know why this lack of file upload capability is not discussed more. IMHO, it's a critical feature for an HTML5 compliant browser.
As close as I could come to finding a solution was to first upload files to a third-party site (say email to Picasa) using an app specifically written for that purpose, then modify the private family website so I could later download the files from the third-party site to the family site. I implemented it. It’s a clunky solution. Not only that, but it makes the information available for all kinds of data mining by the upload service and potentially public. No other iPhone user in the family likes it.
Another potential solution I investigated was to use a custom protocol prefix that would automatically launch a third-party app directly from the browser so the user could pick a file and automatically return to the browser after the upload completed. However, the third-party app demo I tried out (aurigma) wanted to know my location before it would perform the upload. WTF? What’s my location got to do with anything?
Otherwise, how did I like the iPhone 4S? I found the lack of flash, Java, and other third-party plug-ins slightly annoying, the need to give Apple my name and address in order to use the App Store more annoying, and the surprising difficulty in downloading free apps without giving Apple my credit card number a big annoyance. I liked the hires video. I didn’t even try Siri. (Although I talk into my phone, the idea of talking to my phone doesn’t appeal to me.)
In summary, the file upload issue was a decisive deal breaker. After trying out the solutions above, I returned the iPhone for a refund. I’m sticking with my Droid a while longer.