A couple people have PM'd me asking how i got my CelticsBlog avatar back.   I'm not sure when this feature broke/changed, but I noticed tons of people no longer had avatars.  I was unsuccessful in uploading a new image.   I was unsuccessful with linking to a new image.   My guess is it has something to do with a new size/dimension requirement?  
Anyways, here's what I did.
#1 - Found an image I liked
#2 - Re-sized it so that it was 65x65.  The forum lets you select pre-defined images of actors and I noticed those images were 65x65.  I noticed one person (Gainsville Celtic) had a 80x79 image so maybe 65x65 isn't a requirement.  I just know it worked for me.   I did this in photoshop by making a 65 pixel by 65 pixel composition and then adjusting my image to fit in it.  I saved it as a .jpg.   
#3 - Uploaded the image to imgur.com and got a link to the .jpg.  I imagine any image-storage site would work fine.  I tried uploading the image directly in avatar settings, but it was giving me an error.  So I uploaded the image to imgur.com instead.
#4 - In profile settings I selected, "Specify avatar by URL" and plugged in the imgur link to my jpg.   See here:

If that works for you, good.   Not sure what changed in the feature, but that's the only way I could get it to work.  Figured I'd pass that along.