From a user standpoint:
A logo is good, it identifies that an addon belongs to the Ace3 brand, that its configuration will have a similar look-n-feel, that it will be easy to update, and more likely than not, be more updated.
From a distribution standpoint:
I'm not convinced that every addon embedding AceGUI-3.0 should be including a graphic file (the logo). In fact, AceGUI-3.0 is already big enough (120 kb or so in total file sizes) that I do not want Ace3 to be forcefully embedded (discussion was in another thread) if I so choose to install Ace3 addons disembedded.
I am strongly against the idea that Ace3 should always be embedded, no matter how small the Ace3 libraries are written to be. And 120kb is just AceGUI-3.0, I haven't included the other parts of Ace3 yet that are commonly included such as AceEvent, AceAddon, AceConfig, AceDB, AceConsole and AceLocale. If I run 8 Ace3 addons, I definitely do not wish to load 1 mb of code that I only need to load once: 120 kb.
Adding a graphic file to the core embedded distribution may be counter-intuitive to keeping Ace3 small.
From an author standpoint:
I don't care whether there is a logo or not. It makes no difference to my code.
From an aesthetics standpoint:
The blue, red, black, flowery, etc designs, and even the paradox cube are good. But I feel we are going a step too far. They must look good even at small sizes of say 12x12 in a small corner, and any detailed flowery stuff will not be seen. I think Snago's one is the best here, as it is a simple monochrome logo:
It will be small in file size (as it is monochrome), and it will look good even scaled at small sizes, because of the 2-color contrast. It doesn't have to be strictly black-n-white, it can be darkblue-and-white and it'll still be fine.