*chiming in*

I haven't done any movie playing on my iphone, but I plan to when CorePlayer (TCPMP) releases their mediaplayer for the iphone since it will support all kinds of video format and is very cpu efficient, comparatively speaking. (IE: The Coreplayer on my Treo 680 plays more videos formats and at better framerates than mplayer on my N800)

But for ebook, the Books.app application is really very good if you can convert your book to a format that it can read (currently only html and txt. PDF and RTF are on the pipeline). The size of the screen, crispness of display and the smoothness of control is quite a bit better than all other devices that I have which use passive touchscreen (ie: N800, treo 680, 650, sony n73, tapwave zodiac...). I've used FBReader for a bit and it's quite nice, but I end up using the iphone so much more (that I've even bothered to lookup utilities to convert pdf and mobibook formats to html) because of the iphone's better form factor and control.