Notice: this information was written when Microthemer version 2 was current. On Dec 26th, 2014 version 3 was released with a completely new interface. Some of the information may be redundant, but as much of
the functionality remains the same in version 3 we haven't deleted this post.
I tried to manually create a microtheme for Ubermenu (because of the difficulty selecting menu dropdowns in Microthemer) using a copy of the Woocommerce microtheme and raw css from http://wpmegamenu.com/customizer/ but found it would not import correctly.