Rated 4 out of 5 stars

Great Add-on. I will never forget any birthday. Easy to install and handle. Also it is good that it's still under development. The developer is active!
Some features it misses are planned for the future, take a look at the website of the author.
Some features it misses may depend on the development of Lightning and the Address-book, which are not under control of the author.

A workaround for the fact, that it needs a year entry in the contact, is to type a fixed impossible year into that field. I type the year "1900" into that field if I don't now someone's year of birth. The displayed age is 111 years in 2011, but be sure, I don't have anyone in my contact who is that age :-)

DisasterArea
Germany

This review is for a previous version of the add-on (0.8.0).