I recently bought a Samsung Galaxy S that I saw at a very attractive price. I went to the store and they told me they had the last one on display. I inspected it, it looked good, so I thought why wait if and until they get another batch.

After getting home I noticed two things. First, it had eclaire (Android 2.1) so it must have been on that shelf long enough.
Second, the 4 “dock” icons on the android launcher were burnt in and were clearly visible on flat white and gray backgrounds. It was mostly visible on the gray notification screen. In fact this isn't really a burn in but rather a diminishing of the led power, but I will use that term because it closely resembles the fault.

After a quick search I found that the problem appeared to other users too, and some with usage as less as two weeks. Now the icons on the galaxy are not customizable and the phone I bought (eventually I returned it because of this) was probably constantly on on the shelf for years but today I noticed something on the N9 that alarmed me and made me write this post.
I had the phone on my desk playing with qtcreator and it was on the multitasking screen for two minutes or so when my app showed up. On the gray background, the impression of the nine windows was more than clear. I panicked at first but after a while the shadow faded away. It was nothing serious fortunately but as most of us here do not have much experience with AMOLED screens I thought I should share it.
My advice: Do not get excited with the low power consumption of the amoled and leave it on unnecessarily. The nokia clock on the sleeping screen is moving around constantly for a reason. Do switch from two column switcher layout to three column every once in a while to level the wear, especially if you use the switcher a lot. The switcher is the only screen that shows always about the same pattern (4 or 9 whitish windows on dark background mostly) and it is more usual to the switcher and look at it for some time. Feed is mostly black and letters and icons change constantly, and who stares at the launcher more than a few seconds.