It's also significantly affected the degree to which fans interact with tabs, which point you to different content at the top of the Page.
According to data provided to Mashable by PageLever, tab engagement has dropped off 53% since brand Pages began adopting Timeline.
The findings were drawn from approximately 500 Pages with more than 10,000 fans apiece.
You can see tab engagement begin to decline on Feb. 28, the day brands were able to opt-in to Timeline. There's a steeper leading into March 30, the day all Pages were forced to convert. The regular spikes you see in the chart are mark activity on the weekends; users tend to explore Facebook pages more deeply on Saturdays and Sundays.
Why the general drop-off? PageLever founder Jeff Widman believes it's a combination of two things: That brands can no longer set a custom tab as their default landing page for non-fans, and Tabs are less visible in the Timeline layout.
"Without the option to set a custom tab as the default view, most users will never see a tab again," he says. "We’ve heard from several users they didn’t even realize tabs still existed with Timeline."
What does this mean for brands? It's difficult to say. The data doesn't necessarily prove that people are spending less time on tabs beyond the custom landing pages of yore, but with the low visit rates, it may mean that brands will devote less resources to developing content on their tabs and more to the content that appears on their walls.
Facebook declined to comment on the findings. One source we spoke to within Facebook pointed out, however, that the trend could be attributed in part to the content modification tools Facebook released with Timeline.
For instance, brands can ensure that content remains more evergreen by pinning posts to the top of a Page rather than relegating it to a tab, as they might have before.