Since early 2008 we publish traffic stats per Wikimedia wiki in detailed reports.
In the past 4 years the relative proportion of page requests per project did not change much. All projects received more traffic, more or less in proportion to their earlier size. Wikipedia share rose from 95.7% in July 2008 to 96.4% in January 2012. Most of this relative gain was at the expense of Wiktionary which fell from 1.5% in July 2008 to 1.0% in January 2012.
Here are updated diagrams about the breakdown of page requests per project, first in absolute numbers, second in share of overall total:
Click image for slightly larger version