Included in the EXIF data, it should tell you the focus distance for the shot, as well as F stop, ISO, shutter speed, body, and so on. I have that lens, but seldom use it. I will set up a test next week to see how the one I have appears at the edges.
I see Canon have 3 separate L series 24-70 zooms. The original that I have, and that you were using, the new version II of that lens, and an F/4 version. Only the F/4 version has OS. The f/2.8 versions do not. http://www.canon.ca/inetCA/subCategoryHome?msegid=2&catid=17&scatid=72
Facebook is not my favourite site. I have an account I opened years ago to be able to see other people’s pages but I have not done anything with it. It has been a while since I did much with Flickr as well. I had a pro account my ISP paid for, and when that deal expired, I just continued on with the free 200 photos part. At other sites, I have observed uploading an image with more pixels than they display results in the display not looking optimal. Uploading a relatively small image has three benefits, re-use beyond the web is difficult, uploads are faster and the image will look its best because it is not compressed when displayed. I spent a couple of minutes playing with Facebook. I see it will scale images down to about 600 px wide if you display the page in a small window, images grow if you expand the window but wide monitors are typically 1920 px wide and they display a banner on the right side of the image so you are probably limited to 1200 px, give or take. I use 640 px for the width at another site, I think I would use the same for Facebook if I were posting there.
Sharpening is one of the last steps of post. After resizing, since resizing affects sharpness. Different image sizes need different amounts of sharpening. Printing needs more sharpening than images going to a monitor because of the printing process and flow of ink.