OrderedList has conducted a Content Management Survey recently. You can see the result that WordPress is by far the most broadly used system. In general, people seem relatively satisfied with the CMS they have, though there is definitely room for improvement.

Overall, only 12% of respondants indicated any dissatisfaction with their current CMS, while 38% said they were very satisfied. Expression Engine was notable because the low level of dissatisfaction, and the high rate of ‘Very Satisfied’, even though the software costs money.

Source: Content Management Survey Results