In breaking down the statistics for the period of December 2005 through January 2006, over 1.9 million domains are using PHP, and the number only continues to climb. In February, the upward trend continued and usage jumped up 1 million domains more. March, however, has only seen about 100,000 additional domains making the total 21,439,178. On the server side of things there's never much fluctuation and it still sits steady around the 1.3 million mark.
PHP usage took a hit in usage around the beginning of the year, but it's coming back quickly and will soon be back up to the 23 million domain usage soon.