Yeah you create the variable in the assignment and make sure it is visible.
What I quite like to do in cases where there is only one piece of data the user is providing is to use the following in the relevent transition on the task to pick up what they enter in the "Comments" field:
wt.workflow.work.WfAssignedActivity act = (wt.workflow.work.WfAssignedActivity)self.getObject());
wt.workflow.engine.ProcessData data = act.getContext();
name = data.getTaskComments();
I personally wouldn't worry about the name uniqueness, I certainly won't be if we implement this. Someone else may be able to tell you how to if thats the route you want to go down.
Regards,
Toby