For awhile, everyone was talking about stickiness in online applications. Stickiness is the word commonly given to attributes of an online service that make users continue to return.  Sometimes it is used to describe tactics simply to gain repeat usage, like current sports scores or horoscopes–in this case, I'm taking sticky to the next level, the one that makes people willing to continue paying for a recurring service and not cancel.  Ultimately, this type of stickiness is most important, because it ties to a revenue stream!

There are three primary types of sticky:

1.  Data.  If you've gone through the effort to import and create a lot of data, and risk losing the data by using a different service, you are unlikely to want to start over somewhere else.  Examples:  newsletter services like Constant Contact, fitted clothing site MyShape.com

2.  Relationships.  If you have made friends and connections in one community, you may not want to start from scratch elsewhere. Example: Facebook–why would you want to start searching for all of your friends in a new community, even if the community were more targeted to your specific needs or interests?

3.  Prestige or Status:  If you lose the special phone number or URL that indicates long time membership.  Examples: phone services, email providers, AmEx "member since…"

Companies that find a way to make a paid service sticky usually are able to build powerful and reliable revenue streams.