How many usage hours should I get on my iPhone 4?

I'm wondering how many hours of usage I should get on my new iPhone 4. I've had it for about 6 days, and I'm getting about 6 hours of usage and 8 hours of standby. That's if I unplug I in the morning after charging it through the night. My last charge, I unplugged it before I went to bed after it sat at 100 for awhile. I let it sit through the night, and right now it's 7:15 pm. My battery is at 52% and I've tried not to use my iphone very much because I was cautious of the battery. My usage is 3 hrs 34 min. My standby is 15 hrs 42 min. That is after I let it sit through he night off the charger until now. Is this normal battery life? Or is mine defective? I don't know what to expect because this is my first smartphone.