Yes you pay dues annually. The rate is different for each resort and you pay based on how many points you own. The dues cover maintenance of the property, salary and benefits for the staff, utilities, insurance, property taxes, renovations, transportation to the parks, the cost of Member Services, etc. Dues go up about 3% per year, sometimes more (sometimes a lot more) and sometimes less. They can also levy a special assessment of up to 15% if they need to cover something extraordinary but that would be a rare occurrence.
Here is a table listing everything that comprised the 2015 dues at each resort:
http://dvcnews.com/index.php/dvc-program/financial/2015-resort-budgets
And here is a chart of the dues (expressed as the amount per point) over time:
http://dvcnews.com/index.php/dvc-program/financial/annual-dues-by-resort