Comment on LicenseKeeper

You may also use SerialSticker. Version 1.0 was released just today.
See this page in MacUpdate:
http://www.macupdate.com/info.php/id/24305
It has a nice interface and is free.
It's a pity that it can only store licence numbers. It would be nice if it could include other categories: passwords, e-mail accounts data, credit card numbers, etc.
Maybe in a future version...