Yes, thats what I meant. My basic idea was this. A list of protected applications are maintained. For example, we add contacts and conversations into the protected applications list. So hereafter, whenever we try to open contacts or any other protected application, the phone asks for the lock code before opening the application.
I have requested for such an app since I bought my N900 and never saw something like this for maemo.
I have some nosey friends who try to take a peek into my contacts and messages whenever they get hold of the phone. So this is to discourage that. Here, they can still check out my phone,but cannot open protected applications without entering the lock code.

Thanks for taking this into consideration. I'll be looking forward to something like this.