Froyo has not been officially released. What you are hearing is the UNOFFICIAL RELEASE of Froyo that has be hacked by dev for the likes of the Nexus, Hero and Moto Droid. There are known bugs in it, if you go into the Nexus one forums, you can see a list of complaints with Froyo. The Nexus One, which will be the first line of phones to get Froyo is still waiting for its OTA update.
Edit: I will say enjoy your new EVO and not think about Froyo until HTC announces it. Another thing to note, before you get FROYO, Sprint will need to go over the update and include its own bloatwares to the boat. From HTC record, don't count on FROYO anytime soon. Example inludes the Hero, Magic, Eris' update to Eclair took months after it was released in January 2010. HTC claims that because Sense UI is so integrated into the OS, it takes them time to do the update.