And since you've run half way, you might as well turn around and run all the way back... :-)
Half marathons are well worth training for and doing I reckon. I am looking at running some myself either later this year or next year.
It's at about this distance that things really start to change - this is where the excess weight just fell off me. This is where I really started to see improvement in my fitness. And this is where to start to realize that the longer distances are achievable, and you don't have to be from Kenya to run them.
Yeah you're right...You definitely transfer to using fat a fuel when you start running these distances as well.