i am missing that feature too. i used idisk a lot lately and they still have some bugs to fix there. with win xp and safari i often can't select any files after clicking upload.
also the web interface for the public folder is pretty poor and exactly the same as it was in .mac. that means you can see your public folder and files on your iphone, but you are not able to open any of them.
try out yourself by visiting
http://public.me.com/username
if you have set up a password type in "public" as user and your password when asked