I am not an expert in project planning, but at a minimum they should include:
- a list of tasks;
- details regarding what those tasks involved (not just one liners);
- a deliverable for each task;
- the accountable party;
- the dependencies between the tasks; and
- estimated durations of each task.
Some of the junk project plans that I see from vendors are very sad. I am not sure if they are poor planners or if they are just trying to keep things ambiguous to close their sale. I suspect it is both.
Notice: I mentioned that we are developing project plans before the sale. A detailed project plan and a detailed statement of work should be part of any significant IT contract. What I have traditionally seen take place for the first two months after a contract is signed would be better handled before the contract signing so both parties have a common understanding of the initiative.
Candid CIO 
I e-mailed my comment.
This story really re-iterates the importance of having a true project plan:
http://www.channel3000.com/print/4725884/detail.html
In my view a SOW included the commitments (read “promises”) that the internal personnel are making to each other. I submit that it is MUCH more important to make the promises to ourselves before we make them to vendors!