I think its a fabulous idea. I think profiles are pretty useless. Theres never really multiple users on a phone.. theres the owner, and the person that they lend it to for a second to make a call, check the weather, look up a phone number, or get an address (or something similar)
Profiles are pretty useless. Why would you need to create an entire group of settings for someone who might use the phone a handful of times.
Setting one guest mode that you can customize accordingly would be wonderful
I dont have anything to worry about as far as text messages and stuff, but in general they are private. If i was in a meeting with people and someone needed to the borrow my phone, i would rather know that this random stranger CANT do anything.. I mean, i'm not handing my phone out to people on the street randomly, generally they are business people, or friends of friends.. but still. Its nice to keep everything a little sequestered.
Its a great feature that wouldn't impede the use of those who have no use for it, but would add a load of functionality to people who do need it.