See this article for some good reasons to track your inventory online.
See this article for a detailed tutorial on how to use this feature.
To create a personal inventory, go to this page and enter your inventory name ('Rich Personal' for example) into the box that says
By default, nobody else can see your inventory except you. There will now be a new button on every page to allow you to add items to 'Rich Personal'. I use this feature all the time. This feature also adds a new column to all the checklist pages called 'Have' which shows you whether you own the item already or not.