Although we are not quite there yet, it looks like we are one step closer to a permanent root solution on the HTC EVO 3D. Developer eugene373 has successfully achieved "perma-temp" root for the EVO 3D's sister phone, the Sensation 4G, and it seems that many users are having success using this same method on the EVO 3D.
While previous temporary root methods are unstable on the EVO 3D and generally not for the faint of heart, this developer has found a way to prevent the Superuser binary and Busybox link from getting deleted before a reboot – an issue that many users have been experiencing. In his own words:
…what I did was enable the $Path to /vendor/bin which is in the Sensation & Evo 3D export PATH.. Any Calls made from this point either be SU or Busybox don't get deleted nor touched from any App requesting the SU Binary!! I've tested this with alot of apps & the Root sticks in place..
While this method still does not stick after a reboot, it is more stable than what we have seen so far. Still, as is the case with any tinkering, if you choose to attempt this method you do so at your own risk.[xda-developers]