OK, I have the answer. How exciting! Usually I just leave people sarky comments ;)
I use / have used a plugin for iPhoto called FlickrExport – it makes Flickr show up as an option in the ‘Export’ window in iPhoto. When you select all the photos in a set, it seems to keep them all in that order in the export window – so I would assume this means that when they upload to Flickr they’re all in that order as well. I just did a brief test of this and that seems to be the case.
It cost me £12 (around $24). There is a demo version which will allow the upload of 5 files at a time, appending some demo chat (Uploaded with FlickrExport etc) but should do the trick in terms of trying it out and seeing if the ordering works for you.
If so, happy days – buy it!
Holler if you need any help.
Sev