Pop quiz: which of the following has an OEM digitizer and which I replaced with an Ebay one? Don't cheat by looking at the scratches, because one is obviously brand new, while the other ones are scratched. But in terms of light reflection I personally cannot tell the difference.

Now I recently bought all three N900s, so there is a chance they could all have aftermarket digitizers.

All three of your digitizers seem to have the polarizing filter. Do you happen to have bought a spare one, or do you remember if it was completely transparent or a bit dark?

A definitive test will be to use two digitizers or one digitizer and one polarizing filter/polarized glasses and look through both of them while turning one of them around the axis perpendicular to it's surface. You should notice that in a certain relative angle (x) no light passes through (completely black) and at an exactly perpendicular angle (90° + x) the darkness of both glasses is about the same as one of them.

So I bought another digitizer from the same seller. Same as-new condition, except there was a minor flaw. If you look at the pictures below, you'll see that the speaker design is different in the two screens. One has two tabs and the other has two springs. Now the digitizers in the picture are the OEM ones, and the N900 frame actually has 4 sets of pads to accommodate either the spring or tab design. Sorry I did not take pictures of the Ebay digitizers, but they look identical to the OEMs, down to the printing, sponge gasket, colour and everything else.

Ironically I received two different digitizers from the Ebay seller as well, the first one with tabs and the second one with springs. On the spring Ebay digitizer of the springs was completely bent, however given the tight space between the digitizer and frame it still makes perfect contact. And it is far more sensitive and accurate than the OEM.

I've tried the test you suggested, and nothing much happened with four different digitizers (2 that came off the phones and 2 Ebay replacements) EXCEPT that when rotating the colour would shift from green to purple at certain angles. So that might mean the Ebay replacements are polarized as well.

I usually don't bump my own threads twice in one day, but this new digitizer is night and day compared to the used OEM one. It is SO much more precise, every tap registers perfectly. It really feels like a brand new N900 now.

I also applied a Zagg invisible shield on it, and it still feels excellent. Pro-tip: For the cheapest Zagg price, buy a large one, and cut your own. From one $30 iPad 10in Zagg invisible shield I covered the screens on 2 N9s, 2 Sensations and 1 N900. I took our the N900 bezel, traced it out, and carefully cut it.

Now I know this is the second digitizer I bought. But the first one went on my other N900 that is not on my daily driver, and I did not realize the difference it made.

I just purchased from this guy:
http://www.aliexpress.com/snapshot/219926811.html

I don't know if its really OEM but at least looks pretty close to the original one...

It was well packaged, and I had no issue with the purchase.

I bought two digitizers from ebay seller yallstock. Avoid. Both of them don't work.

(Actually the first one I tried did respond a bit, the second one didn't respond at all)

Mine are still working, although the N900 is not my primary phone anymore so it gets light use when reading books. Tested the sensitivity and it's good...

I just installed a cheap N900 digitizer I've bought on ebay, and it's now obvious that the quality of these non OEM parts varies.

Compared to the original one, this digitizer feels less solid (the plastic is thinner and it bends when you press a point in the center of the screen), the the touch is now much less sensitive so you have to press a lot more and it often doesn't register a touch.
The overall feeling is also quite rough when I slide with my thumb so I imagine that the coating material on the outside is different from the original.
Polarizer filter definitely is not present as well, the digitizer looks transparent and not dark like the original one. Maybe now without the filter the contrast of the screen is lower in this situation that's the last problem.
The speaker was also missing and I have to move it from the old original digitizer.

I'm going to order another one from the ebay seller you suggested and I'll let you know.
Let's keep this thread updated, our N900 are very precious but with the passing of the time they are getting older and the digitizer is one part that often needs to be replaced.

P.S: by the way, do you guys know a place where to get the Philips 00 size screws that are used on the N900 so I can change them before they broke? (apparently I haven't found them on ebay) Thanks!

EDIT: by the way, this is the digitizer I'm speaking about (bought around two/three months ago but installed just yesterday) : http://www.ebay.com/itm/Original-Tou...-/220809160699
Unfortunately I couldn't buy the one you suggested because the seller doesn't ship to Italy

Nokia used to sell them as spare parts but are discontinued. When I replaced broken display local repair shop helped and gave me screws -- they were used, but still in better condition than original one after I unscrewed them :/

Just a suggestion

Thank you for your suggestion, I'll try to ask in a repair shop.
Anyway an online shop would still be the best solution, if it exists..