Sorry? You can upload multiple files in the same HTTP POST. Just add several <input type="file" to the same page (and hope you don't hit max_post_size). That can be done with javascript.
Or do you mean uploading half file now and the other half on a second connection later?
I mean uploading an arbitrary number of files, without having to pick each one individually. For example by picking a directory, or multiple files fron the same directory.
Sure, HTML can give you 100 "choos file" fields. but who wants to use that?
-- daniel