Laptop Mag reports they noticed significant drops in battery life after installing Windows 7 on netbooks. The worst case was with the Toshiba NB205, this notebook lasted 9 hours and 24 minutes under XP but lasted only 6 hours and 15 minutes with Windows 7 installed. The site believes the reason for this is because Windows 7 drivers aren't as efficient yet as drivers for previous versions of Windows, and that consumers may want to hold off on upgrading if battery life is key.
The biggest surprise was the loss of battery life. When we ran our standard battery test on the Toshiba NB205 under Windows 7, it lost more than 3 hours. Under XP it got an amazing 9 hours and 24 minutes, but with Windows 7 it only lasted for 6 hours and 15 minutes. Installing new Win 7 drivers from Toshiba only resulted in an extra half hour or so (6:53). We also noticed a bit of a drop-off with another netbook we tested: the MSI U123. This time it was less dramatic: 8:14 in XP vs. 7:41 in Win 7.