Sorry, I'm jumping in really late here, but I'm very curious about your setup, as I am thinking of doing the same thing. However, I read a review of the thunderbolt display saying that it wouldn't work very well with the iMac. He said he couldn't extend the desktop to it, so couldn't use it for any additional real estate. However, in looking at your photo, it seems you are doing just that. Did you have any trouble configuring it to extend to the extra display?
I don't know where you read that, but I would urge you to not read anything else written by the same person / organisation / publication.