using 2 seperate devices

I'm new to the iphone world and need help! Me and my husband both have iphones. We've upgraded to ios5. I don't understand how the apple ID works etc. If our apple id is the same on both phones, how do I keep all our pictures, contacts etc seperate when I backup and sync using itunes? Do I need 2 different apple ids? Also what about icloud. Do I need 2 seperate icloud accounts? For some reason all my contacts are merged with his contacts on his phone now! What a head ache. I'm so confused!!!