Many people have been complaining about their battery life in OS X 10.8 Mountain Lion. It is reported to not be effecting everyone. A small decrease in battery life is to be expected as many new features in Mountain Lion will run in the background. For example notifications and iCloud support will be constantly updated which will be using CPU power and thus decrease battery life.
Apple has acknowledged this problem and has asked users that have already logged a complaint, to send their log files so they can work on a fix.
No doubt Apple is working on a fix for this problem that is most likely to be released in OS X 10.8.1. We would be interested in hearing your experiences with battery life in OS X 10.8 Mountain Lion.