[QUOTE=FatBaldGuy]
I thought we did away with this concept in the 1940’s or 50’s when the ignition key was invented.
[ul]
[li]Other than not having to carry around an ignition key, what is the advantage to this?[/li][li]Assuming the door is unlocked, can anyone just get in your car and drive off, or is there some other security safeguard in place?[/li][li]What do you do in a situation where you want to listen to the radio, but not have the engine running?[/li][li]With a keyed ignition, you can’t remove the key unless the engine is in Park. Is there any similar kind of interlock with this keyless system?[/li][/ul]
In short, I don’t see the appeal, and it seems to me a lot less safe and secure. Do any of you have a car with keyless ignition, and how/why do you like it?
[/QUOTE]
Ignition keys pre-date the forties by a fair bit. I think you are referring to starter switches with were on the way out in the 40s and 50s.
To answer your questions
As has been mentioned, you don’t have to dig for a remote or a key to get into or start the car. This is very handy if you have items in your hands when you get to the car. The system is programmable to unlock just the door you grab, or just the two doors on the same side of the car as where the “key” is, or all doors.
No, someone just can’t get into your car and drive off. Compared to a straight key type system security is greatly enhanced. (Volvo specific information) First off the “key” has to have been programmed to the control module. To access programming you have to access Volvo’s central data base to get the pin codes that will allow you to get into programming mode. Not something the average car thief can do. In order to start the car, the computer that controls the keyless entry/ keyless start has to trade a pass word and response with the car’s central computer (The duck walks at midnight / It might rain on Tuesday) They assuming that both units are satisfied that all is OK the central computer trades another set of passwords with the engine control module. As a final check both modules look at the serial number of the ABS control module. If all of that passes the car starts. Could it be cracked? Sure but it would be a lot easier to tow the car away.
Don’t step on the brake, and push the button for 1 second and the car is in accessory mode. Press the button for 2 seconds and the car is fully on.
Engine will not shut off unless in Park or neutral. If you open a door with the engine off in neutral, the warning gong from hell + a nasty message in the digital display both warn you to put the car in park.
One other advantage to this system. You absolutely cannot lock your keys in the car. 
ETA:MrFloppy I got five bucks that says your BMW has way more than 7 computers. Like three to four times as many.