Just to underscore the points made in the section above, and to highlight the importance of planning and communications to the CRM implementation process, here is a list of some of the classic mistakes we unfortunately see at more client sites than not:
Failure to get someone to take ownership of the process from start to finish.
Failure to involve your stakeholders, especially the end users, right from the requirements gathering stage.
Not having a focus on the current business process, the intended business process improvements, and the specifications for a system that will effect that change.
Thinking that implementing a CRM means buying CRM software, installing it on a server, and then telling the people who need to use it.
Not making a particular and continuing effort throughout the project to communicate the benefits specific to each user and stakeholder, to ensure their buy-in.
Biting off too big an initial project phase, or simply proceeding as if phases are for sissies...