They weigh about the same as a decent netbook, but cost more. Battery life is similar: 9-11 hours, not counting standby time.
They do not weigh the same as netbooks, unless you have some sort of super light netbook. Taking one at random, the Samsung N110 is 1.2kg from what I can see online. The 3rd generate iPad weighs 0.65kg, quite a difference.
The quoted figures of ~10 hours you'll see for the iPad is while making fairly constant use of wifi. Is your 9-11 hours on the netbook with a similar workload ?