I can also report the same behaviour. My portable install on USB drive just support cover art Visualization.
It would be very nice if the portable install also supported G-Force, WhiteCap etc... - in case,of course, they are actually installed on the PC executing MC.
In that case I would decide to have the whole main library on my USB drive and then using one of the several PCs that I have for playing and saving my play statistics and even modifying audio/video tags. Now that USB powered HD are available is a very nice that your Audio/Video/Photo Library can travel with you toghether with a complete MediaCenter installation.
Today the only thing which is preventing this to be realized is that portable install lacks some plug-ins / visualization support, so that it is very unlikely that the portable install may be chosen as the main MC installation. Another weakness is that portable install does not remember the initial dimension of the MC13 window.
Despite this, MC13 is great. It really makes me happy using it.