Documentation has appeared for BES 5 on the BlackBerry website, this is great news as there are some cool features that have been missing to date.
My top 3 are HA, monitoring and administration.
To date to achieve HA with BES you needed to buy an additional product, such as Neverfail, and configure hot swap servers. BES 5 includes Neverfail style clustering out of the box, so no more down time for BlackBerry users.
With BES 4.1.5 the BlackBerry Monitoring Service was released, it presented much need statistical information about servers and devices in a web based console. BES 5 builds on this.
BES 5 administration is all web based, so no more rolling out management tools. The BlackBerry Web Desktop Manager has also been updated and allows users to provision there own devices, so long as they are enabled on BES. There are also now over 400 built in policies to choose from.