#1 Easy access. The blogs and the blog administration tool must be easy to access and so must the RSS reader used to read RSS feed items with. They must be accessible from any computer or mobile device with web browsing capabilities. Cumbersome autentication procedures must be avoided.
#2 Ease of use. The administration user interface must be really simple to use. Even simple usability issues will eventually discourage users from blogging unless they are really dedicated bloggers. There should be big buttons for creating, editing and publishing posts and simple editing tools.
#3 Single point of administration. The administration must be user-centric, meaning that employees must be able to administer all the blogs they own or contribute to from one point, using one single administration tool that allows users to easily toggle between blogs (as a comparison, in MOSS 2007 you have to navigate to each blog to create and edit posts, which is really cumbersome).
#4 Freedom of choice. Employees must be able to use their RSS reader of choice. If employees cannot use the same reader for internal feeds as they use for external feeds, it will cause frustration and they simply won't read internal RSS feeds often enough or at all. If an internal RSS reader is available as one of the choices, it must allow subscription to external RSS feeds (besides being easy to access).
#5 Mobility. Employees must be able to blog and read blogs and RSS on the go, using mobile devices. Preferably, it should be possible to create and publish post via e-mail, MSS and SMS in addition to via a web interface.
#6 Tagging. It must be able to tag and categorize posts so that employees both can manage their blog posts and allow users to navigate posts by subject or interest area. Preferably social tagging that suggest commonly used tags should be supported.
As a matter of fact, all of these pre-requisites are in some way related to easy of use.