There isn't an official answer to that question just yet (I'm sure HTC and other manufacturers are being bombarded with "when are we getting Gingerbread?" tweets and emails right now), but don't worry. The EVO will get Gingerbread no matter what. It just may not be from an official channel, that's all.
There's already a bootable 2.3 build, which was hacked together from the just-released Gingerbread SDK, up and running on the EVO. The folks at xda-developers are behind this, obviously, and though they don't have a fully functional port yet, you know it's only a matter of time before they do. Many of the best EVO devs are tackling it and they've already made a lot of progress. I'm sure it won't be long before we're all flashing a freshly baked Gingerbread ROM on our rooted EVOs!
It's actually pretty likely that HTC will be giving us an official 2.3 update (it will probably be our last big one), but you know for a fact that it won't be before xda does.[xda-developers]