Here are my very first impressions:
The screen is incredible. It’s lower DPI than my iPad and iPhone but, for some reason, the sharpness is striking.
I’m used to lugging around 15” MacBook Pros; the Retina MBP feels substantially smaller and lighter. (If you’re lucky enough to own a MacBook Air, this thing will feel like a tank — albeit an impressively fast tank.)
Lots of apps need updates to support the Retina display (including, I’m sad to say, mine.) Chrome and Sublime Text 2 both render pixelated text. This is the most jarring aspect of using the device so far. On iOS, apps are full-screen; on OS X, they typically aren’t. Pixelated and Retina-aware apps coexist. They overlap. The result is visual confusion.
Most websites don’t support high-DPI displays. As with the Retina iPad, web images are nearly always pixelated. The few exceptions are worth a visit. (Cabel Sasser, you are God.) When I redesigned my blog, I intentionally made it text-only — this was my cheater’s path to Retina glory.
The new fans are quite nice. That said, I have a small home studio; it’s actually going to be harder to EQ the laptop fan out of recordings now that there isn’t a single frequency to target.
The thing runs incredibly hot at full steam. The F8 and 7/8/9 keys can get very hot to the touch. I’ve never really complained about heat from my Apple laptops, but the Retina MBP definitely pushes the thermal envelope.
I have no good reason to use it, but a 15” screen in 1920x1200 mode is hilariously fun. Compared side-by-side, the 1680x1050 resolution looks as good as the native 1680x1050 MBP that my friend loaned me for the past few months.3
I expect it will take half a year or more for the native apps I regularly use to add Retina support. (Some will probably never see an update — I’m looking at you, Twitter for Mac.) The web? Well, it’s going to take a lot for the average site to care about high-DPI.
Bottom line: the Retina MacBook Pro is a beautiful new beginning.
 I tend to upgrade my laptop every three to four years. Alas: I’ve had a run of truly bad luck. A couple years back I was mugged and earlier this year my car was broken into. In both cases I lost my laptop, iPad, and headphones. Yikes. This time, dammit, it’s not gonna happen. This one’s gonna go the distance.
 I have no idea how this happened.
 Thanks so much, Marc. You’re a champ!