I just started using Portfolium theme (WPShower) after using PhotoNexus, only because I wanted a cleaner look and it suits the type of work better (I hope...) - while Photonexus is fine I had a problem re slideshow loading which is not an issue on their demo site & which I was never able to resolve fully.
You can see the problem at : http://www.raviswami.com/blog
(click on a thumbnail to view a portfolio page)
After switching to Portfolium, I noticed its slide show has the same problem - again not noticeable on their demo site, which is hosted on their own server.
Queries on their forums and elsewhere have led to a blind alley.
Basically, adding galleries and slideshows is not a problem, but when they display (ie after you open the page) images will load in a vertical stack for a beat, before settling into the expected slideshow, as per their demo site - this was the same for both themes.
The blog I need help with is www.raviswami.com.