I know this is an old thread, but I thought I'd post my experience here rather than start a new one.
I have been eyeing mechanical keyboards for a long time, but in my area it is very hard to find them in stores to try them out. I have been considering the Razer, DAS, and Mathias models for Mac, but uncertainty has kept me from doing much of anything about it.
I was at Best Buy yesterday and saw that they had the Black Widow Ultimate 2013 for PC there, and decided to pick it up. Best Buy is good about returns, so I figured I'd try it out and if I like it, I can order the Mac version online and return this one.
I already had the Razer Synapse software installed on my MBP since I use a Razer mouse (Death Adder, horrible name but a great mouse). I was surprised and pleased when I plugged in the keyboard. The OS X dialog asking me to identify what type of keyboard it was popped up. As soon as I did that, Synapse immediately recognized the keyboard and started downloading the drivers/kext/whatever for it. I did have to close and restart Synapse in order to get everything working. Once I did that, Synapse showed the keyboard with all the customization options, backlighting, etc.
What was pleasantly surprising was how easily the keyboard worked with the Mac using the Synapse software. The media controls, volume controls, etc, all work, which I was not expecting. There is no screen brightness control on the PC version, so I can't do that, but the others seem to work fine.
I used the Mac keyboard preferences to swap the Option (Alt) key and Command (Windows) key. In the pref pane, you set Option to Command and Command to Option. That way the center Windows key is the Option button, and the Alt key is the Command button, just like the normal Mac keyboard layout.
I'm not sure if it's my imagination, but it seems like they keys on this keyboard are smaller and/or closer together than most other keyboards I've used, and this is taking some getting used to. But overall it's a really nice keyboard. The feel and sound of the keys are amazing, and I can tell I'll be able to type faster on it once I get accustomed to it.
TLDR - I really like this keyboard. Even the PC version is a totally workable option for a Mac user.
Before I make a final decision though, I have to ask the community here - has anyone compared this keyboard to the DAS and/or Mathias Tactile Pro? If so, what are the differences?