One of the casualties of the 1.1 release was the experimental upload progress helper. Unfortunately it didn’t work on all the platforms we support and it was a source of numerous bug reports. After talking with Sean, we decided to remove it from rails’ core.
For those of you who were using it, the code was extracted to a rails plugin. To install it just run the following command and everything will be back where you need it../script/plugin install upload_progress