Ok, shame on me.
Clearing the cache solved the layout problem. Thanks for your help. I'm now going to try the facebook stuff with this new upgrade.
Meanwhile, you can check what i've done so far with Showkase : manuel-luce dot fr
I'm not quite satisfied with some of my layouts, but i will try to play further with this new upgrade and make the perfect design (to me !)
By the way and as a suggestion, you should make a blog post to show some of the websites using Showkase. I've been looking on the web to find some, but except the demos on your site, i found nothing. Too bad because when you start customising a theme, it's always interesting to see how other people used the product to fit their needs.