I still use a Macbook Pro 13 for portable use but as for my main workstation, I recently switched to a PC.
Main reason being that Aperture was not being updated properly, wanted to a new tower for more space and speed, figured would be cheaper to move over to Lightroom with a new far more powerful PC.
This is exactly where I stand too. After the announcement of the new Mac Pro. I've decided to build a beast PC. My primary use for a workstation is photo editing along with video occasionally. It's probably going to cost as much as the new 2013 Mac Pro, but I wont need the external peripherals (Thunderbolt as aPPLe is pushing), everything will be inside accept for a Synology Diskstation NAS. If anyone is curious I'll be gunning for either the Intel 4930k Hex or a 3.5ghz 4770k quad OC'd to around 4.5ghz.
My current 2010 3.2 Quad Mac Pro is not keeping up where it should be and I can't upgrade it without breaking the wallet. Things I was looking to upgrade were adding a Sonnet Temp Pro PciE card with dual SSD's in a Raid 0 and adding a USB 3.0 card, and going from my current 12gb to 32gb ram. The only CPU I can upgrade to is the 3.33 Hex which is stil a good CPU, but lets face it, if I'm gonna pay $550+ for a cpu that I can't even OC, I might as well get my bang for my buck on a PC rig.
I will still be buying the new MBP Retina refresh when it hits the shelves for my personal uses. I'm convinced that Apple notebooks are the best having been using them since 2008. Before that, I was using HP's.
I'm saddened by the fact I going to switch. But in the end, It's what will help me with my workflow in my photography business.