For me, there are 2 types of ToDos - checklists and reminders. Checklists include things list:
• books to read
• movies to see
• items to pack for a vacation
• stuff to fix around the house.
Reminders are the things you do at a specific time (like on your way home):
• pickup milk
• go to the bank
• drop off a prescription
• mail a letter
I like to see these things in my calendar so I can plan around them, but I don't want them to be included in my personal or work calendar. Especially if I'm sharing my calendar with others.
My solution: create a separate calendar called Reminders. When I create a reminder (e.g. pick up milk at 5:30 p.m.) I enter it in my calendar and assign it to Reminders. When the time comes, I'm notified with all the features of a calendar appointment (popup, email, SMS). Don't worry about the end time of the appointment — you're only concerned about being notified once it starts.