Select your flash drive, in this case 'Yosemite Sam' (see image below).Click Continue, and the following screen is displayed. Launch the installer and it will display a splash screen. The rest of the installation is actually quite simple.Shawn 'Doc Rock' Boyd set up a similar drive with legacy operating system installers and Yosemite, which he uses not only to try out the new OS, but to work with his consulting clients. Note that you might want to create several partitions.Once complete, I checked the logical partition to make sure that it was indeed bootable (see image below), and then it was off to the races. My flash drive came with some oddball DOS-based format I erased it in Disk Utility, then created one full-sized partition set up as Mac OS Extended (Journaled). You just need to make sure that it's properly formatted and partitioned. I picked up a PNY 64 GB USB 3.0 drive from Amazon for US$26 perfect for installing Yosemite, Xcode 6, or other apps that you'd like to test with OS X 10.10. Now, while all this is going on, get your USB 3.0 flash drive ready to roll.Once you've logged into the App Store, the download begins and you just need to wait for it to complete. For developers, this is simple - just log into the Dev Center with your credentials, click the OS X Yosemite Developer Preview button to open the tab for Yosemite, and then scroll down and click the button to redeem your code to download the installer from the Mac App Store. Download the Yosemite beta installer, also known as 'Install OS X 10.10 Developer Preview'.Instead, you can easily install Yosemite on a USB 3.0 flash drive and have your development/testing operating system available in your pocket just a reboot away. But you should never, ever install a beta operating system on a production machine - otherwise known as 'my only Mac' or 'the Mac they gave me at work'.

Developers are already testing the new OS, and the general public can begin testing soon in an open consumer beta. OS X Yosemite has a lot of people excited, and for some good reasons - a new, more iOS 7-like UI, AirDrop that works with iOS, calling from Mac, and a host of other really useful and fun new features.

Install yosemite from usb