Is there a way for me to manually arrange the cards in the corkboard?
For example, if I wanted only two cards in the top row, with four cards beneath them, rather than three and three.
I do not believe you can do this in Scrivener 1.x, but you will be able to with version 2 which is available in a few days 
Check the section on the corkboard in this blog entry of Keith’s… literatureandlatte.com/blog/?p=133
Eddy
You mean something like this?
Yes, like that.
Is that version 2, then?
Yes, this is a screenshot from 2.0.
Okay, thank you
Since it is Amber to anticipate it, I hope not to break the NDA. So, I would add that this new version of the corkboard is smooth, effective, highly inspiring. A picture in nothing compared to the actual use. It is the first index card app that you can really replace to the real things, without feeling contrained in chains.
Paolo