1) OVI Store is Nokia's "App Store", however it is not yet enabled for Maemo 5/N900. The OVI Store icon just takes you to a "coming soon" page on the N900. However, like others said, the application manager has access to repositories that you can install stuff from easily - and there is also maemo.nokia.com and click Maemo Select for some officially picked stuff. Eventually OVI Store will be the official, commercial outlet for additional apps, but Maemo being open, of course there will be other community delivery channels as well, and one can configure new ones of these to be shown in the application manager too.

2) The screen is plastic because the resistive screen requires it. The up-side is that it can also be used with a stylus for precision browsing or the like. But because it can be used with a stylus, I would recommend a screen protector. Vikuiti DCQ-160 is my choice, easy to apply and reapply without residue, doesn't seem to affect either visibility or touch with either fingers and stylus. And like someone said, because the screen is recessed a bit, the protector sits comfortably in that recession and becomes nicely a part of the device.

3) I don't know about those videos, were they pre-production or something else, but YouTube videos work great on my phone from the browser. I haven't done any extensive testing, but what I have used, has played well and the experience is just like on a desktop browser. Very nice.

6) I have it in my pocket (inside a Nokia's official non-model-specific accessory sock) all the time, no problems. But of course mileage may vary.