Facebook users tend to be more interested in keeping close tabs of family, friends, and their favorite brands by "liking" everything from celebrities to books to causes than is true for Twitter users.
Seniors are fast-growing segment among social network users -- in 2011 33% of Internet users 65 and older were on social networks and Facebook tops the list and 4% of people over 65 in the U.S. are now using Twitter. In 2009 only 13% of seniors were using social networks. This means in two years the number of seniors using social networks more than doubled.
Twitter is most popular among African Americans and Latinos. Fully 25% of online African Americans use Twitter at least occasionally, with 11% doing so on a typical day.
Additionally, Twitter use by internet users ages 25-34 has doubled since late 2010 (from 9% to 19%) and usage by those ages 35-44 has also grown significantly (from 8% to 14%).
Twitter does not bombard you with app instructions (but there are many widgets and third party services you can use to step up your game) nor does Twitter come with the same social pressure to custom design your look. A Facebook page without a profile and cover picture looks lazy and unappealing, Twitter right out out of the box looks like well, thousands of other Twitter sites - clean, simple, but just fine. And, Twitter actually allows users easier tools for a greater visual customization than Facebook does.