There seems to be a problem on the D90 and D7000 that involves the "blinking green light" (the FLASH write indicator), but is different from the "blinking green light of death" on the D70. With the D70, the camera fails to work at all; this has been acknowledged as a defect by Nikon, who will (would?) fix it for free, even on cameras out of warranty. On the D90 and D7000, the camera works, but the following symptoms may appear:
* With camera in off position and both memory card and battery installed (it seems batteries installed in a grip have the same problem), the green light flashes; and battery drains rapidly (far more quickly than if camera were left on).
* The on/off/illuminate control doesn't work correctly--specifically, switching to "illuminate" may fail to illuminate the LCD backlight when it is off.
* When camera is first turned on, LCD (meaning the thing on the top, not the monitor LCD) comes on and stays on, until a photo is shot. Then, the monitor remains on all the time (until dismissed with the playback button) rather than appearing for 4 seconds (or whatever your setting is) and then disappearing.
* The two-button format and two-button reset functions do not work (at least on D90). You can format the memory card from the menus, but not with the two-button control.
What SEEMS to be the issue is that the off/on/illuminate button is being "stuck", either mechanically or electronically, and thus the camera acts as though it is being held in the "illuminate" position. What seems to work (it works for me) is to slide the switch to illuminate and then QUICKLY to off. If the green light still flashes, try it again; it may take several times. Once you get it in the good state, then DO NOT use the illuminate feature again.
Your mileage may vary, of course. I've heard enough reports of this issue that it's probably something that Nikon ought to look into as a design defect; so far, though, I've never heard of them fixing this for free (for cameras out of warranty).