I bought a rentina mbp a few weeks ago and I've been using it daily since then. I just can't see the productivity increase above and beyond windows that everybody claims..
I'm roughly the same productivity wise, maybe a bit better since now I can use the computer in bed (kinda hard with a desktop) but that's not unique to OS X.
I love the laptop, don't get me wrong.. the hardware is awesome but OS X.. Windows.. they're all the same and I don't see the point of installing it on a hackintosh..
I guess it depends on what you do.
A quick example, I do a lot of back and forth emailing with clients. For detailed replies when I can't catch them on the phone/skype, I'll reply with an audio file.
I used to use a PC app for it. The best one I could find, you had to open the software, record the audio, export the file, open web browser, click attach in Gmail, then send.
On OSX, the Voice Recorder app is in my menu bar. I get an email, open it in Sparrow, click the record app, drag the file into Sparrow and send.
We're talking 30 seconds to a minute difference, and that adds up.
Another example is text expander. I have all kinds of canned support replies hot-keyed. You can hot-key common code snippets, like wrapping div's or an href tag. I couldn't find anything like that on Windows, and I'm using it constantly.
There's a lot of little time saving things I'm finding. As far as writing not much difference. But with little things I'm finding a lot of useful time savers.
As far as installing OSX on my PC, I was curious to see if it worked, and curious to see how I'd like working with it. It only cost me the price of a Mountain Lion upgrade ($20) and an hour to install.
Now that it works, why not? I've got Windows and OSX to choose from. I've got better hardware, a lot more upgrade options, dual 28" monitors, etc etc for less than half the price I'd pay for a comparable Mac.
I'll most probably be looking into Mac Books for my next laptop though.