all style, no substance
I live in Phoenix and stayed at the Clarendon for a one-night downtown getaway with my girlfriend. Based on our experience, I'd recommend stopping by for a drink and a taco, and to look around and enjoy the cool, funky ambience and then leave. In fact, I'm convinced that the management and staff there don't want you to stay anyway. 
First and foremost, don't buy a Groupon for this place, ever. I followed the instructions to book online and the website didn't accept the code and didn't have the capability of showing me what dates were available. When I called reservations (3 different times) the desk person (yes, you really are a desk person at a hotel) was not able to tell me any dates I could book with the Groupon because they "don't have access to that system". At the Clarendon, apparently you can't make a reservation by calling reservations. After going around and around with this and never getting a straight answer, it's apparent to me that Groupon's are accepted or declined on the whim of the manager on any given day. When I was finally granted the privilege of using it, they still said no Groupon rooms were available but they could convert it to a gift card and I could apply it toward the room that way. I'm not making that up; that really happened. By the way, this was a Wednesday night and walking back to our room late that night we saw many rooms with the window-shades open that we're obviously empty. On, check-out, I was under-credited for the groupon, no, excuse me, the gift card by $80 and I had to ask the desk person (yes, you really are a desk person at a hotel) to adjust it correctly. Don't buy or try a Groupon here.
On a positive note, the decorators have done a nice job making the most out of this old hotel. It's visually appealing; with just the right amounts of retro vibe and modern urban funk. The room was crisp, clean, and quiet, and the bed was very comfortable. Free Wi-Fi with no passwords or hassles at a hotel, imagine that! The restaurant, lounge, pool, and rooftop deck are all unique above-average features.
Now for more bad stuff: The air-conditioner units are way over-complicated. I'm guessing most people don't want to set timers and programs on a remote in their hotel to get air, especially in Phoenix. There's something to be said for a simple thermostat. Forget convenience here. You have to go to the desk and talk to a snotty desk person (yes, you really are a desk person at a hotel) to get anything; ice, pool towels, snacks, you name it. Except coffee, and when the in-room coffee maker didn't work in the morning we weren't a bit surprised and had a good laugh and didn't even consider calling about it. 
So, for us the Clarendon didn't get the basics right and that's why I can't recommend staying here. Customer service, air, things like that. The staff are very busy being cool and have attitudes that far exceed the reality of their surroundings. In a sense they're getting their wish... if you treat your guest like a nuisance, eventually they'll go away.