We will be upgrading the site to the latest version of WordPress on Thursday, December 20th. The upgrade should take about thirty minutes and then it will take roughly another hour or two for the upgrade script to process each site. We will begin the process at 8 AM and it should be done by noon. During that time users should refrain from trying to interact with their sites.
You can learn about the new and updated features at http://wordpress.org/news/ Probably the most notable improvement to users will be the new media upload interface. The new interface reduces the number of clicks involved in adding media and also makes it much easier to create photo galeries.