The Cost of Switching
A startling discovery is how much it costs for someone to learn that some of the menu items are in different places in Microsoft Office and OpenOffice. Even more startling is the fact that it costs nothing for the same people to learn where the same menu items have moved between revisions of MS Office.
Adapting to any new system takes time. It may have additional dependencies—a new web app might need a new back-end database, for example. Or, it may need staff training.
Be objective when looking at your switching costs. If your staff needs a lot of retraining to switch between different word processors, then they are probably not efficiently using their current tools. If this is the case, then you might consider switching to something completely different, such as a web interface to a template system—something that gives a much more task-oriented approach.
Skills on the system administration side are slightly different. An administrator needs to be familiar with all of the capabilities and quirks of a particular piece of software. This may require some form of training, which it may be offset somewhat if there is a strong developer community.
Much business software requires some degree of customization and often support from an external organization. If a second source is available for this, then it is often cheaper. This applies to both open and proprietary software; however, it is more common with Free Software.