BuddyPress.org

@gazouteast

Okay, I’ll add a few thoughts and ask a question or two here as well–in no particular order of importance.

• When describing the avatar-uploading behavior in point 2 of your your OP, you state that:
  

  the cropper tool fails to grab the image and displays only a black 88px x 16px background “bar” in the avatar viewer.

  That behavior can indicate one or more issues. Here are a couple.

  First, it could mean that one of the dimensions of your image file is too small. By default, BuddyPress sets the small avatar at 50 by 50 and the large avatar at 150 by 150. So, if your source image is smaller than 150 on at least one of its dimensions, you could have issues with creating the large avatar. If it is smaller than 50 on at least one of its dimensions, you could have issues with creating the small and large avatar. You will see black for any missing pixels, meaning that the cropper has to add pixels to bring the image size p to the minimum required dimensions

  Second, it may be that your server is running too old of a version of the GD image library.

• In your post just above this one, you talk about using the auto-upgrade feature for WPMU. I never use the auto-upgrade feature when upgrading WPMU or BuddyPress. It is simple and quick enough to manually upgrade them and it gives you more control and assurance that it is done right.
• You mentioned that you do not have any additional BuddyPress plugins installed and activated but that you do have a couple of WPMU plugins activated. When trying to figure out issues with your setup, you need to distill your environment down to the lowest, common denominator. That means deactivating all plugins except BuddyPress and using the default BP theme. So, although you only have the Akismet and Default Blog Settings plugins activated, I would suggest deactivating them when trying to figure out what is going wrong.
• Are you on a shared or dedicated server? Talk with your hosting firm to see if there is some javascript-based application that the hosting firm has running on your server that could be interfering with the basic JS operations in WPMU. For instance, a MooTools-based application that has a conflict with the jQuery framework used by WPMU. Although this is a very slight possibility since you’ve indicated this behavior has happened on three different hosts.