It's from this presentation (20MB PDF!) that Nokia did a couple of days ago - more specifically from the Nokia Research part of it.

I doubt it's something we'll see in the shown form, though - more like usage concepts they're working on.

Sources and context are important. This is a slide taken by a public presentation made last Thursday in the Nokia Capital Markets Day 2008.

Not a leak.

The slide belongs to a presentation of David Rivas, Vice-President, S60 SW Technology Managment.

Note: I was just as curious as you about the slide since I didn't know about it. I found the source through a search starting from http://maemo.org/news and the blog post from JS Manrique - http://omag.es/blog/2008/12/06/new-conceptual-maemo-ui/ . In cases like this it's worth checking maemo.org and doing a little research.

EDIT: Ah, chlettn found also the link while I was writing this post.

So pathetic... I'm starting to think that it's some kind of Apple forum Considering number of rumors per inch

The first part of the PDF is mostly marketing blurb. Impressive nevertheless

Here some references to the pages of source for verification of reader and also so you see the high quality version.

Note I use page numbers based on what Evince tells me they are; not the page numbers the document uses (they are slightly out of sync).

Source: page 216 & 217 of presentation.

Source: page 261 of presentation.

The layout would no doubt change when the device was rotated, to best fit a landscape orientation.