If you have read that not all EN-EL3e aftermarket batteries are the same then this product should allay your fears. Apparently some newer Nikon cameras such as the D90 need to communicate with a chip in the battery pack using the third battery terminal - if this communication fails, the camera rejects the battery and won't operate. The packing from Hama for this battery is marked with an "also for D300/D700/D90" sticker, so it clearly knows about this issue.
A note about first charging. As with most Li-Ion batteries, the pack is supplied discharged. (The terminal voltage on a digital voltmeter read zero.) When first put on the Nikon charger, the charge light flashed a few times and then stopped. Charging stopped after about a minute. I have seen this behaviour with mobile phone batteries, so no immediate panic. Everything was OK after the AC power was removed, the battery taken off the charger, put back and the AC power restored. The battery charged fully and subsequently the next charge was OK from the word go.
On the camera, the battery was at first rejected - the battery level meter was flashing with only one bar showing. But as another reviewer (Jorge) pointed out, you just need to be a bit persistent. I took the battery out of the camera, put it back in and all was then well. The 'shutter count sinced last charged' function on the D90 works fine, as does the charge level meter. Performance so far has been good.
Overall, I'm happy. I have awarded it 4 stars because of the minor niggles on first use, but this is one of the cheapest aftermarket batteries for the D90 I could find so if it lasts anything close to the Nikon original (for charge capacity and lifetime) it will have been a good buy.