I've been taking the message from Google #IO13 to heart and trying to use Google as my darkroom. I have a metric ton of photos from some family vacations that I figured I'd upload and see what Google's Auto Awesome processing would do to them.
Google+ gives you a method to drag and drop photos onto the browser based uploader but that isn't really a great method for bulk uploading tons of pictures. I tried lots of pictures at once and it froze up. Google Drive might be an option but the 2 services aren't connected that well. You can share from Drive to Plus but Plus doesn't treat your photos the same way. Photos stored in Google drive aren't part of your albums and don't get processed in the background.
As far as I know, the best method for bulk uploading from a desktop is to use Google's Picasa software. In Picasa you go into Tools –> Bulk Upload. From there you can choose your folders and upload straight into Google+ for processing.
This all seemed like a great idea. My upload speed at home isn't all that great but I didn't really care. Just get the process going and leave my laptop on for as long as it takes. Then it stopped working and I got the message saying "long term bandwidth exceeded." I was able to upload the picture seen here via the web based uploader so apparently I am not completely locked out. I can't tell you exactly how many pictures but I'd say a few thousand.
From some brief Google searching, I'll be in Picasa Jail for 20 to 30 days. So, use Google as your darkroom but be careful about how quick you expect it to work.