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I have a 15" MBPr that I sit on a Targus cooling pad/adjustable angle stand that has USB port replicators (x4) on the back (Never have had any issues with heating though). Through that, I run a USB wireless Logitech trackball mouse and 500gb USB HDD that I use for backups. My 100gb+ iTunes Library is in Apple's iCloud via iTunes Match. I just download playlists and movies that I want at any given time. I originally planned to get a 27" display but decided I don't really need it for my purposes and prefer to just work on the laptop display.

I LOVE my setup! I can easily move around the house or take it with me with no concerns.
 
I use mine rMBP with 23" LG Monitor with wireless keyboard and magic trackpad as a desktop. Laptop "mode" when i'm out of home or on the bed.
 
As others have said the Macbook Pro makes a excellent primary computer. Able to provide many functions for your specific uses. Personally I use my Mac as a desktop and a laptop. For iTunes I just store it all on my HD since it only takes up 50GB. My setup at home consists of a Asus 24" external monitor connected to my MBP via DVI. I also have Bose Companion speakers attached to it, also I rest my MBP on a rain design mStand so I can use my MBP as my second monitor which I highly recommend. Topped off with a Apple Wireless keyboard and Logitech Anywhere MX mouse. Creates a nice desktop for me and when ever I need to take it somewhere I unplug it and off I go :).
 
See my sig :)

My late 2010 13" MBP is my main work computer. I bought it new with 4gb ram and 250gb mechanical HD. Now ram is 8gb and HD is 500gb SSD.

I am a SW developer working in Python/Django/Linux environment but I design, develop, and test on my own little laptop just fine. I work at a startup so we all have our own machines. Sometimes I run Ubuntu via VirtualBox but mostly I'm fine w/Mac OSX and terminal. At work I'm hooked up to a 24" monitor with external keyboard and trackpad. Back home it's solo with just the power cable...using it for entertainment, pay bills, read/write emails, etc...

Oh and I have an old iMac too my kids use when they're over. But I consider this my main. I get the urge to upgrade once in a while and probably will when hell freezes over or I get some extra spending money :)
 
I use a MacBook Pro retina with a 3TB external drive, of course I upgraded everything on it so it's extremely powerful (It cost about $3500.)

I also use a 2012 iMac which is also pretty heavily upgraded.

Basically, I see no reason why you can't use a MPB or MBPr and your main computer. I am thinking about getting a Thunderbolt display when they are upgraded, you never can go wrong with more screen space haha.

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Oh yeah, I also use a Magic mouse (Trackpad can get tiring.)
 
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