Last week I downloaded a Nuxeo 5.6 build. After downloading, it took me only a few minutes to get the instance up and running - pure vanilla with the exception of using Postgresql 9.1 as the database. I have only had a bit of time to play with the release and explore some of the changes but I have to say that my first impressions are very favourable.

• Running Nuxeo 5.6 on the same server as I run 5.5 using the same components (DM, Collab, and DAM) the 5.6 server started slightly faster (this was not a scientific comparison but the results seem consistent); the start time on the server went from 21 sec (5.5) to about 19 sec (5.6); server spec - see below
• I felt the responsiveness (performance of the UI) was improved significantly (again this is my out of the box impression -- I may be crazy). I did find that the default navigation tree jumped a little (like a pixel shift) and that was a bit disconcerting. However, remember I am not looking at released code and so there is probably much last minute testing and tweaking underway in the Nuxeo development bunker
• The UI takes on a much more polished look than its predecessors. This is reflected in updated graphics and in Action menus that just look more professional (it's too bad this new look doesn't seem to extend to sub-actions - at least out of the box - although I haven't dug under the covers and maybe this is easily configured)
• Reorganization of the default DM UI makes for (in my opinion) better use of available space - some of that's achieved with icons and some is achieved through a combination of better contrast and better presentation of simple data (like current document state and contributors)
• Every time I visit the Admin Center there is cool (and more importantly useful) functionality exposed - I only sped breifly through this section - enough time to see a number of new tabs, functions and the same UI improvements as DM
• I didn't, however, see any outward facing improvements in the DAM interface (anybody help here - am I missing something?)
• The cookie trail seems to have shrunk in size, which personally I like, because I always like to see the entire path up there, but it may be too small for some
• One part of the UI I would really like to see streamlined is security administration. This is one part of the UI that has been with the product for as long as I have been using it, and in my opinion it's just clunky - needs to be more intuitive and easier to manage. Not simple I know, but given the other UI improvements hopefully somebody will turn their attentions to this area of the UI in an upcoming release
• Really like the new icons although it will take a bit to remember which one is which (this isn't a complaint, rather an observation)
• Just haven't had time to make it through Social Collaboration in any detail but the new dashboard looks great and although it may seem trivial, I really like the idea of a built-in voting system
• I know there are numerous internal improvements (some obviously reflected in ui and load speed) to look forward to, but not this time around

The pre-release code seems extremely stable - out of the box, running in less than 15 minutes, and no crashes! Spending a few hours looking at 5.6 scratched the surface but was well worth the investment in time.

Server Spec: i7, 8 cores, 32GB RAM, SSD Boot/App disk, 7200RPM SATA for data, running CentOS 6.2 64 bit.