I don’t know how strict the demarcation will be, but I’d like to have this just to separate my e-mail app from everything else on the phone. I need to keep my e-mail secure so I have a lock pattern, but then when I’m out and about and checking maps, playing podcasts, wanting to take a picture, etc., it’s a hassle to have to do my crazy unlock pattern every time. It would be nice to just have one profile that has a secure lock pattern and can access the e-mail app, but then have no pattern for the profile that can view all of the other apps or take a picture from the lock screen.
What I think would be great would be an elevated user and a regular user, that aren’t necessarily separated. What I mean is, I let my friends use my phone from time to time, and it would be nice if I could have an unlock pattern that only unlocks a custom set of apps and another that gives full reign. If you want to make a call on my phone, I give you regular level user privileges that forbids use of GMail, etc, but I can unlock to have full access for myself.