All I've seen so far is Fabien's slide where, starting with slide 14, the OpenERP 8 roadmap is discussed.

http://de.slideshare.net/openobject/the-future-of-openerp-open-days-2013-keynote-presentation-fabien-pinckaers-ceo-openerp

I Heard that many bugs and issues faced in V7 is completely fixed and V8 is going to be a ready hit out of the box....and to be launched in 2013 itself

Soon news about OpenERP 8 documentation here and there.

If anybody have a link to the V8 documents please share. I'm looking forward for some features which we couldn't meet in V7 and were required by few of our clients

At Open Days there was a presentation about upcoming API changes, and a part of it can be found in Youtube:

youtube.com/watch?v=j04bzVmxeu0

While the video quality is not perfect, you can still see some quite interesting new things.

I dont think there will be much difference in document of v7 and v8. Instant messaging is the mail feature added up in v8. We can download latest v8 from http://nightly.openerp.com/trunk/nightly/src/.