Siri is that lovable artificial intelligence unit that is all the talk these days. The feature is one of the key selling points for Apple's new iPhone 4S. However, Siri may may not be all that is seems for those who like to protect the information in the iPhone with a passcode or password.
If you setup your iPhone with a passcode then by default Siri can still be activated by holding down the home button and allowing whoever is using the phone to use all of Siri's functionality, with the exception of driving directions and email. There may be other functionality that is prohibited but I did not discover anything else. This means that anyone who has your phone can still send emails, read and send SMS and iMessages, make voice and FaceTime calls, see notes and much more. This may not be a big deal if you don't have sensitive information but what is your phone gets lost or stolen? Of course, you can deactivate Siri in your passcode settings if the phone it locked but that deactivates Siri all together.
I always use a passcode, on all my electronics, and I know many others who do also. When you turn Siri off with a passcode it turns Siri completely off and won't even activate when your hold your home button, while this seems obvious I think it can be handled better. So, if you use a passcode on your iPhone 4S you have a comprise, use Siri or don't use Siri. It's not often that when I check the weather I unlock my phone and then ask Siri, I just open the weather application since it's right there after the phone unlocked. I am not going to unlock my phone and then tell Siri to text someone or send an email.
I believe Apple can make this better, for example, right now if you phone is locked and you ask Siri for driving directions or to check email it will ask for your passcode first. I believe this can be implemented into other parts of Siri like SMS/iMessage, making calls and sending email.
This way those who have a passcode can still use things that don't pose a threat to valuable information like weather, stocks, Wolfram Alpha, simple questions and more. I think it'd be a toss up for calendar and notes information, either way would work for me.
Doing the above would allow those who have valuable important information that they want to keep confidential can still do that, while easily using some of Siri's features. I have information on my iPhone that must be kept confidential and I know many other people do as well, for us Siri doesn't help that much. I certainly know that people who are in the same situation as me would appreciate these type of settings for Siri.