In our case, 10 percent is what we hope to save with our solar charging, and of course a lot more with the PV roof. Its supported by many organisations, most visibly the Guardian... but I see that even the Sun is supporting it!
10:10 is also about a sort of discipline.. cycling more, walking more, growing more food. Even if it doesn't help the planet literally or measurably, it will make us improve our lifestyle to be more healthy and less consuming.
One of the things you can do is buy an OWL meter, so you can rigorously check the amount of power you are using on a daily basis.
PLEASE Go to the 10:10 Web Site and Sign up... and make your decision of the ways you might cut that 10%... or 20%. Its gotta be more than replacing a few light bulbs.