For the curious, I just applied the update myself. Am going on vacation for a week tomorrow, so I'll root when I return.
Took maybe 5-7 minutes to complete. The Evo rebooted several times during the process. My SD card mounted without issue afterwards. I'm hoping this solves the issue, and if so, major kudos to HTC for fixing it by launch day!
There are 4 boxes to use in the defense of liberty: soap, ballot, jury, ammo. Use in that order. Starting now.