Here is what I sent to apple (
http://www.apple.com/feedback/ipad.html):
"+At my company we are very excited at the iPad and how it can improve our workflow. Like many others I have talked to, I plan to use the iPad for work and home (play).+
+One feature that I found that is glaringly missing is the ability to password protect mail, calendar, and contacts. Let me give you a use case example:+
+I have my iPad that I use for my work email, calendar, and contacts. Also, I have music, movies, and children's apps on my iPad. Lets say I take my family on a road trip and I want to play a movie on my iPad and give it to my 5 year old daughter. What is preventing my daughter from accidentally opening my email and deleting mail. Same thing for calendar and contacts.+
+What I envision is a parental security feature where I can password protect any application of my choosing on the iPad. Also, it would be great if there was a simple "toggle" icon I could press to turn this on and off.+
+Thank you for your consideration.+"