Netbooks and laptops battery wear

I have been looking at buying a netbook for a few weeks now. The main reason for buying this was for battery life. The Netbook I am looking at has been reported to achieve 4+ hours easy with high usage. But something that disturbs me is the wear on the battery. People (Using third party software) have seen a 5% wear on the battery in as little as a week and some people see stupid things within months.

How accurate are these 3rd party applications for testing battery wear in general?
Are batteries this bad in general?

Batteries are very hit or miss. My Dell laptop is 4 years old and still has most of its battery capacity. My daughter's Dell lost its battery capacity in 2 years, as did my mother's. I did some asking around when I was trying to determine where to buy a new battey for my daughter, and found that some people bought new batteries that lasted years and other people bought new batteries that lasted just a few weeks. I've noticed on some manufacturers websites that they sell separate extended warranties for their batteries, separate from the rest of the computer I mean.