You're pretty much figured out how to do it. The main problem is you usually don't have access to the size of the uploaded file until it's done uploading.
There are workarounds for this:
Enabling APC, you to access this information if you include a field called "APC_UPLOAD_PROGRESS" and use apc_fetch() for retrieving a cache entry with the status.
There's also a plugin called uploadprogress but it's not very well documented and doesn't work on Windows (last I checked anyway).
An alternative is to use Flash for doing it. See scripts like FancyUpload.
Before APC came along I had to write a CGI script in C that wrote information to a text file. APC seems like a much better way to do it now though.
Hope this helps.
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