Finally. I released version 0.1 of my new Mediawiki skin Chameleon today.
For the longest time I used Gumax Horizontal. I liked the color scheme, the layout of the page elements (horizontal menu on top, whole page width for the content) and the dropdown menu. But updates were slow and buggy for new versions of MediaWiki and I did not particularly like some of the changes in the newer versions, so I had to constantly patch it. At some point it became too much and I decided to write my own skin.
Lazy that I am I chose to largely avoid having to write my own CSS and use Twitter Bootstrap instead. Worked out great. Out came a skin with the layout I like and dropdown menus. There are some other nice traits that come with using Bootstrap. Without giving too much thought to that, the skin already seems to scale quite alright on smaller devices, like tablets and phones. But some more thought has to go into this. Another bonus is that it is really easy to modify the appearance of elements (colors, dimensions, fonts). Want a narrower navigation bar? One line in the LocalSettings. Different font size? Same. For a complete makeover just include your own LESS files. Bootswatch.com has some nice stuff.
There is still some work to do, but it is already a fully functioning skin, so I released it as version 0.1. See https://www.mediawiki.org/wiki/Skin:Chameleon
for installation and customization instructions.