One thing I like about the skins feature is the ability to remove it if the user doesn't like the look once it is downloaded. I noticed one yesterday where it completely made the Status Bar at the bottom, invisible.
I've also noticed many of the skins have errors in them. Some of them will display the icon text on the Main Bar, unevenly. If one of the icons is smaller in size than the rest, the text underneath that particular icon will appear slightly above the text of the other icons, so when looking at it, the icon text isn't perfectly straight across the row as a result.
The skin I am using currently is Ubuntu Human
with a red color scheme. The icon size is set to 160%, to make them fill up the Main bar going left-to-right as I'm using a 19" monitor.
UserAgent: Opera/9.64 (Windows NT 5.1; U; en) Presto/2.1.1