Here is a really easy tip for communicating with users.  If you have used the 'alerts' functionality in CRM OD, you will know some of it's limitations.  So instead create a blog called eg 'sales alerts', you may have multiple eg 'system alerts/tips', whatever.  Make sure the blog can be accessed by RSS, most blog sites like blogger.com can.  Then simply create a global webapplet in CRM On Demand, in the administration/application customisation and put it on the users home page (you'll need admin priviledges).  Create different blogs for different audiences, eg marketing.  It is a very easy way to send messages to the field (users), and can include links pictures, etc, like any other blog.

In the picture below you can see how effective it presents my own blog.

(Right click and view if too small...sorry)

Now if you have a problem posting to a public domain blog like blogger or wordpress, you can download free blogging software such as wordpress, and install on a server behind your firewall, therefore only your secure users can see your alerts.