If you hadn't yet noticed, we've added Mass Uploading for two of the most commonly requested sections, the Administrative File Uploader and the Gallery.
Clicking the new "Browse" button will bring up a dialog box that you can multiselect files in (using SHIFT or CTRL while clicking).
This will make uploading files significantly easier rather than having to do the old "select file, click upload, repeat" process which was quite tedious.
I've only just tried this for the first time today. Something appears to be broken, or I'm missing something, or I'm not patient enough, but on both Safari and Firefox I've been trying to upload 2 files. The blue process bar goes full on the first file and then it does nothing. I've let it sit for 5, 10 minutes and nothing happens and the file never uploads nor goes to the second file. It just says "Uploading..."
Oh, dang, yes I forgot I was supposed to check that. I'll do so when I am at home. Perhaps the mac version isn't as up-to-date as the Windows one... that happens.