This issue almost caused me to throw my mac out the window. I LOVE using iWeb to design, but Apple make it virtually impossible to post to an external host- well not that hard to post, but infuriating to update.
Anyway, I found a free app that is very handy for just uploading your changes to the site. It still requires publishing to a folder, but the upload time has decreased drastically.
Check Out:
Easy iWeb Publisher 4.0