One of the best ways to make your site "sticky" is to encourage users to use multiple features.
Encouraging users to engage with more features increases the amount of data they share with you. The more data they share with you, the more you succeed in creating a "switching cost" that serves as an impediment to abandoning your service for one that may offer a similar set of features.
The switching cost exists because in order to start using a site offered by one of your competitors, your user now has to take the time to set up their data on the new site, and often learn a new user interface in the process. This is not something users are very likely to do unless your competitor offers much more value.
Mint and LinkedIn both do a good job of enticing you to share more data with them. Mint asks "How Minty are you?" and answers that question with a personalized score - the highest being 100% - based on how much data about your financial life you share with them. They do this via a simple user interface shown below.
LinkedIn provides a similar user interface that gives you a score depicting how "complete" your profile is. They encourage you to add more data about yourself and solicit recommendations from others in order to achieve a higher measure of "completeness".
Both of these user interface devices are "achievement indicators" that stimulate feature engagement by appealing to a user's ego. As a person with a competitive, Type-A personality, I feel a sense of achievement in seeing that progress bar climb toward 100%. It's not very rational, but it is very real. In striving for this feeling of achievement, I increase my commitment to the service by providing it with more personal data.
So do you want to get users to engage with more features on your site and create a switching cost? Give them a user interface that appeals to their ego by rewarding them with an incremental sense of achievement for each piece of data they give you.