But...but...but it's a dry heat!
We are New Englanders living in the Phoenix area, and all I can say is...I've never experienced such heat and high temps in my life!
Now, of course, we've gone from one extreme in temps to another, but man, it sure does get hot here!
Having said that, it's true, it IS a dry heat and we don't get the humidity like Florida (and even in Maine!) so there's less sweating out here and the air is more breathable and less heavy. I'd compare it more to the heat that comes out of your oven when you open the door after cooking. THAT kind of heat! If we are outdoors in June, July, August and September, you'll usually find us in our swimming pool.
The heat here means business, and you seriously have to think twice about touching car door handles and anything else that's metal. I've noticed many places of business wrap their door handles in some type of cloth, and most outside dining areas have water misters constantly spraying eating areas. Even with that, it's still too hot to dine outdoors in the summer.
The most coveted parking spaces in the Phoenix area in the summer aren't the ones closest to the stores, but instead are the ones where a small tree shades the parking space. Prime parking if you can get a little bit of shade!
And then, like others have mentioned, you get the unpredictable rains in July and August that can rapidly flood areas. It comes down fast and hard, then leaves just as quickly as it came. No soft, pitter-patter of rain here!
Personally, I wouldn't visit Phoenix in the summer. Wait until October through May. Phoenix is beautiful in the winter, absolutely gorgeous temps, and in the spring everything is in bloom and just beautiful!
Now, if you do decide to visit, just try to get all of your outdoor activity done in the early morning hours. Remember sunscreen, sunglasses and sun hats, and to drink lots of water! And spend time in a resort pool! If you're a Diamondbacks fan (or fan of baseball in general) take in a ball game at Chase Field. The roof is closed (unless it's an unusually balmy evening) and the entire facility is air-conditioned. It's a great place to see a baseball game! There a ton of really good restaurants in the Phoenix area, and of course, all are air-conditioned. Like others have said, head north of Phoenix (Flagstaff, Payson, etc.) for cooler temps. Or drive five hours to Las Vegas, which can be just as hot as Phoenix, but you can spend all day inside the casinos!
We are also part of the crowd that spends time in California during the summer-
Disneyland, here we come! LOL! We also go back to our home state of Maine for a few weeks every summer. If you decide to visit Phoenix in the summer, I hope you have a great time!
And while that "dry heat" doesn't feel as bad as the humidity, every exposed bit of a skin felt like experiencing 3rd degree burn!!! One of those things as being "locals" may not notice since they're used to it. 
