When you float an element to the right, then use jQuery UI's resizable widget to make it resizable from the left edge, weird things start happening.
I've put this together:
http://jsfiddle.net/nicholasstephan/kCduV/2/
If you resize the "sidebar", you'll see immediately what I'm talking about.
What am I doing wrong here?
I'd prefer to keep the float:right so the left column takes care of itself.