[skwirl]

You could use OmniPlan to lay out the project and resource assignments for all of your projects in one OmniPlan project file, then jump into the Resource View to see the workload of all of your resources.

To put all of your projects and their subtasks in one OmniPlan file you can create a group for each project, then list all the tasks as sub-tasks. This will allow you to share the same resource pool over all the projects.