While, granted, this doesn't come up often, it would be nice to have it documented somewhere (FAQ 148? FAQ 64?) that the length of the URLs on mood theme images cannot be any longer than 100 characters. It doesn't matter if you use the Mood Theme Editor or do it manually through the Admin Console, it gets truncated on-server, even if with the Admin Console it displays the complete URL immediately after you've set it.
For example, http://www.lynnebaer.com/onehundred/onehundred/onehundred/onehundred/onehundred/onehundred/onehundred/onehundred1234567890.gif gets truncated to http://www.lynnebaer.com/onehundred/onehundred/onehundred/onehundred/onehundred/onehundred/onehundre, when put through the custom mood theme editor.
Nothing big, just something in the FAQs that notes this limit. "Please note that the addresses for your mood theme icons cannot exceed 100 characters. If they do, you will need to shorten them before your custom mood theme will fully work."