Never tried it, but I can't imagine spending more than a night in a bivy or hammock. Aside from the miserable sleeping conditions, how do you keep your gear dry if it rains when using a bivy or hammock?
I agree with the previous poster that saving one or two pounds is not as big a deal on a bike vs. backpacking for example, where the weight is on your back the entire time and it may be worth it to shave a pound off your gear.
I use a 1.5 man tent, non-freestanding. I think it weighs 5 lbs total with poles and everything included. When I was buying I was so concerned about weight, but in retrospect I wish I had gotten a freestanding tent even if it weighed a pound or two more. I would rather have a few extra pounds on my bike and be comfortable and feel secure in a tent, and i like having extra space to store my gear in case it rains.