Can you Copy and Paste? then visit http://www.vimeo.com/1463913 and see how easy it is to hack your Feedburner subscriber count. Won’t take more than a minute or so to add a few thousand subscribers.
I am sure Google / Feedburner will look into the matter and probably fix it soon, you can enjoy it till then however. Even if Google fixes this its very simple to forge the image in Photoshop and display as many subscribers as you want.