I just got my fire TV, rooted and installed a few apps including the firedtv.
I left it over night and realized it never went into sleep (the front led was on). I was able to put into sleep using a keyboard, but I don't want to keep the keyboard near my fire tv all the time.
Do you guys know what is wrong?
Try rebooting your box and without loading any external apps, see if it goes to sleep after a certain time. My guest is that an app is still running in the background preventing sleep mode.
When I first installed XBMC that happened too. I found out that XBMC was still running in the background because I didn't properly exit the app. Clicking the home button on the remote just leaves XBMC running in the background. Exit by pressing XBMC power off button and setting the system power saving timer to shut down at a interval during idle works.