I would have to say the biggest reason that a SharePoint implementation fails is that companies do not take the time or want to spend that money on creating a plan. What happens is a company says I hear SharePoint is great and can do all these things for our business so they purchase and IT deploys SharePoint. After deployment is over they hand over the keys to whoever they deem capable and tell them to create there site and start using it. EPIC FAIL!!!!
SharePoint needs to have a plan and specifically governance. Every SharePoint implementation should have a governance plan a governance plan will layout "the rules" of your companies SharePoint implementation. User will embrace SharePoint if it is easy to use and SharePoint will be easier to use if it has a consistent look and purpose. If every site looks and acts differently they users are going to be confused and frustrated and instead of embracing it will find other way to do something so they do not have the use the site. Governance sets the rules and responsibilities for the site. In the governance is lays out why is responsible for what through the implementation process and beyond. It states how the look of the site is going to be handles in terms of branding and rules on what a department or business unit site can change and what they cannot. It is also going to set organizational rule like what terms (keywords) we are going to use on our site and working with every department collectively so that people are not duplicating efforts and the information that is used by many is stored in a centralized location that everyone can use.
Please contact one of our if our Heroes if you would like assistance with your governance plan.