I have the HTC Evo 4G with the latest OTA update as of 3/10/2010, I am not rooted and do not use a 4G widget. I too have the problem of 4G on at reboot and randomly throughout the day. I get HTC/Sprint's new so-called "helpful widget" that is really not a widget, but is in the notification bar alerting me that the 4G antenna is on, and then have to turn it off. Anyone ever find a solution to this?
This only started happening after the last OTA update. There is no longer a setting to turn off notification, just the checkbox to turn 4G on/off along with a menu item to initiate a scan. I wish it would go back to the original way it worked.