I know, I know, stop the presses: 
Facebook is the most popular app on  Android. The 
statistical  wizards at Nielsen reached this conclusion based on active usage, not total  downloads, noting that the recently-updated  Facebook app has the most penetration across all of Android’s user groups  after the Android Market itself. The fact is at least a little surprising, since  Facebook beat out Google’s entrenched apps like Search, Gmail and Google Maps,  which all had slightly lower user groups in every category. 
Nielsen breaks down the distribution of most-used apps by how many users  opened the app in the last 30 days. So while nearly 4/5th of the Android  population uses Facebook on a regular basis, only about three quarters actually  use 
Google Search, which is built right into the framework of Android. When it  comes to third-party apps, Facebook absolutely kills the competition, with 
Angry Birds getting less  than half the active users that Facebook enjoys from the 35-44 crowd. Other  notably popular apps by usage include 
Pandora, 
QuickOffice, 
Yahoo Mail, 
Adobe  Reader and Advanced  Task Killer Free, despite the latter being unnecessary for almost all  current Android devices.
 The Android Market beats all, but since it’s a gateway to almost all  third-party apps that’s understandable. Strangely, younger users actually seem  slightly less inclined to download apps than their 25-44 counterparts. Among  18-24 year-olds, 89% use the Market regularly, compares to 92-95% for older  users. Angry Birds is also significantly more popular in the older age group, a  fact that lines up with some personal observations. Don’t install Angry Birds on  your grandmother’s shiny new 
DROID this holiday season, unless you’re keen on  hearing a dozen different varieties on the theme of “SQUUAAAAK” all weekend.
 [
via  Androinica]