You don't have a send a message to find out if a person is on an iOS5 device... once you type them into the "to" field, their name will turn blue if they're iMessage-capable. If it stays green, you will be sending an SMS. No quick way to see this for all your contacts at once, though.
I love people. I started using a contact management system decades ago. This list has stayed with me at every job; even at my own company. I'm in sales and marketing. It's what makes me marketable.
Then there is all the businessses I have bought from, church and friends. It's a career full if people. From the days of the original Palm Pilot, this list has transferred to every computer, phone and smartphone. I'd be lost without it.