This is from XDA Developers. It will work on all EVOs as of 1/21/2011. I have rooted three EVOs using this method and it works great. The number one reason to root an EVO is to be able to mess with the processor speed, but it also works great if you want to use the wifi tether apps in the market which only work on rooted phones. Have fun!
Due to some bugs, Unrevoked 3.2 was taken down shortly after being released, but the updated version is now LIVE! So obviously we're going to bring you a video tutorial on how to do it! Thanks to the guys at Unrevoked for giving us this simple solution to rooting the HTC EVO 4G.
LINK TO VIDEO WALKTHROUGH FOR HOW TO ROOT THE EVO
From Unrevoked:
No system downgrading or /data wiping, one-click root, a full NAND unlock and no PRI downgrade.
Nice, right? So here's what you'll need 
◄●REQUIRED DOWNLOADS●►
- EVERYONE: Unrevoked3. Download the version for your OS.
- WINDOWS USERS: unrEVOked modified USB driver
◄●How to Install HBOOT Drivers (Windows Users ONLY)●►
If you're using Windows, you're going to have to install the HBOOT drivers first. You can follow this video tutorial:
and follow along with these written instructions provided by the Unrevoked team:
- Download the unrEVOked modified USB driver and expand it somewhere you will remember.
- Turn off your phone, then boot it into the HBOOT menu by holding power and volume down.
- On your phone, you will have to select HBOOT USB at that menu by pressing volume down four times, then power. Wait until the screen flashes through an “SD Checking” message before pressing buttons; otherwise, the phone will ignore keypresses.
- Connect the phone to your Windows machine with a USB cable and wait for the phone to say HBOOT USB PLUG on screen.
- Open Device Manager.
- Click Start, then right click on Computer, then click Properties, then click Device Manager.
- Under Other devices, you should now see the Android 1.0 device.
- Right click on Android 1.0 and click Update Driver Software:
- Click on Browse my computer for driver software.
- Click on Browse and select the Android USB Driver folder on on your computer, click ok, then click next.
- You should get a status bar indicating that the driver is installing. If you get any warnings, just click Ok.
- Your driver should install.
- Click Close and make sure Android Bootloader Interface is listed under Android Phone.
◄●Instructions●►
- Make sure you downloaded Unrevoked3 for your OS.
- If you're on Windows, make sure you "uninstall HTC Sync or any other program that might talk to the phone over USB (doubletwist, etc). They will cause problems" (Unrevoked.com).
- Plug your phone into your computer with USB.
- Drag down from the notification bar on your phone and select "Charge Only" and "Remember this"
- Make sure your phone has USB Debugging turned on by going to Menu>>Settings>>Applications>>Development and checking USB debugging.
- Run the Reflash application that you downloaded.
- Unrevoked will run its processes. Follow the few instructions it gives and thats it!
You're now rooted!
