Would highly recommend the back-to-back table design for its aesthetic (naks!) and ergonomic considerations. Seriously the concept is worth considering not only for the two 'pogi' points i mentioned above, but will give you a stable platform, i.e., we usually experience minor earthquakes and tendency for CPU's on top of a shelf is to topple over. This design results in a lower center of grav that should give your unit a somewhat stable platform.
My main worry is that, the CPU seems to be installed under the table and this could pose three problems, heat build-up, the occasional nudge or kick from the customers (HDD alert!), and its a PITA when it comes to changing mouse or KB as we have to deal with confined space. I would consider further having a wall underneath, who knows yung magkaharap lalo na sa DOTA, nagkakaasaran na at nagsisipaan na pala sa ilalim! LOL!
Nevertheless, i would consider this design myself (am due to change tables btw, nalubog sa baha eh! water saturated majority kaya humina ung mga paa! waaa!) with some minor changes as i've mentioned above.
PS.
PITA - Pain In The Ass