people "chiming in" here will not fix the problem. a ticket needs to be made into HTC directly.
if you have not already done so, send htc an email and get a ticket started. share the ticket number here and when others see/experience this, they too can call in or submit a ticket. the more people who talk to HTC directly the sooner a fix will be made.
HTC do not read these forums.
All that said, ive a stock non rooted sprint model and i have the same flicker/gradual dim issue. i never ever use power save and the issue was happening from day one. I have seen reports of this on another forum but not much activity was in that thread.
using swype or an on screen keyboard will make it more pronounced as well.