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I went with the Fusion drive for my order. I am currently using a 2011 iMac with 128GB SSD + 1TB HD (this was before they introduced the fusion drive). I love the combination of storage and speed. I think it's the best of both worlds (all my apps are on the SSD and docs on the HDD). Also, I barely notice the noise coming from my HD. Hopefully the new fusion drive (with the PCIe connection) will be even better.
 
Lol, not literally hanging off. But an extra device connected and sitting on the desk. It's a legit question that may bother some people. I know in my office the rear of my desk is exposed, and with my iMac the only wire going to it is a power cable. In that setup I'd prefer not to have external devices around. Though at home right now, I have a TDB with a thunderbolt drive connect to it and sitting filled with media.

No disrespect intended

I have clients who need 10s of TB storage and a clean desktop, so we put everything in drawers and behind doors and vent ;)
 
I have a rMBP with a 768Gb SSD. By the time I also have a Bootcamp partition I'm constantly having to delete stuff off to make room. I'll be getting a Fusion drive because I really need the space. If I wanted lots of external drives I wouldn't be buying an AIO.
 
I didn't go with the Retina iMac, but did go with a new-to-me refurb i7 w/1TB SSD. I can comfortably fit all my working files on it and not have to worry about an external drive like I would have if I went with a smaller drive. I love the speed and silence of an SSD based machine. Yeah, it's a little extravagant, but hey it's a mac, right? :) I had a 128MB SSD on my old PC that I also loved...it was just too small. Once you go SSD there's no going back to a spin drive!
 
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