OK, this is going to be a "duh" moment for most Mac developers, but apparently there are some people who are having issues with setting up a test environment in which to run OS X Mavericks. I have to admit that I was one of those who first started asking if anyone was having success running the latest Mac OS in a virtual machine under VMWare or Parallels. There are some people who claim to have OS X Mavericks running fine under one virtual environment or the other, although most are being rather closed-mouth about how they accomplished it. So, tired of waiting, I decided to do what I've done with previous releases and just create a dual-boot machine.
It's stupid easy to do this:
1) On your OS X 10.8 machine, sign into your Mac Dev Center account, click on the appropriate tab for OS X Mavericks, and then download the OS X 10.9 Developer Preview (click the button, which launches the Mac App Store, and magic happens).
2) While you're waiting for the download to complete, it's time to set up your Mavericks partition. Fire up Disk Utility, click on your primary disk drive and add a partition. I made mine 64 GB (on a 256 GB SSD MacBook Pro with Retina display), named it Mavericks just so I'd be more apt to select it instead of my main drive when installing 10.9, and then let Disk Utility do its thing. This takes very little time, so go enjoy the outdoors while the download continues and try to get some sun.
3) Once the Installer has finished downloading, it should launch itself; if not, go into Applications, find the app named "Install OS X 10.9 Developer Preview" and launch it. Follow the instructions, select the Mavericks partition you created in step 2 as the target for the beta OS and sit back while the installation continues.
4) Now you have a dual-boot 10.8 / 10.9 machine. To boot into one or the other of the partitions, just hold down the Option key while rebooting and select the appropriate one. Of course, that's not particularly helpful if you just have a single development machine and you don't want the irritation of booting in and out of two versions of OS X several times a day. That's why as soon as things are working smoothly with Parallels 8 and/or VMWare, we'll pass along the instructions for setting up Mavericks virtual machines in both of those environments.