I know this was talked about in the earlier RC's but figured I would post it here as well as to not clutter the other forum pages. I started reading the rc5 notes of "custom user 'thumbnail' images" and got very excited but alas.

+1 here.  Now getting close to having a fair few VMs and would love the ability to set custom icons. 

 

Try editing your XML, I use this:

  <metadata>
    <vmtemplate name="Custom" icon="/mnt/disks/HGST_VMs/MediaGrabber/MediaGrabber.png" os="ubuntu"/>
  </metadata>

 

It works for me.