Unfortuantely, there is no way to view the total count of all your active tasks unless you have only a few parent projects and many sub-projects in which case you could use the arrow icon on the left of each parent project to collapse sub-projects and that would add up the task count for all its sub-projects.
Thank you for answering my question over the weekend. I am a new user trying to make this work to manage my home improvements as we remodel our house. I have 36 major projects and am loading up the tasks. I expect to have about 200 open tasks and use the total to manage the backlog. Am I an outlier user that doesn't fit your profile? I would think a grand total feature would be good to add to your product and request you do so.
We will consider adding such option in the future and you're welcome to request it in our Votebox: http://todoist.com/Vote/