Don't setup ad positions more than once.

Great module. Very easy to use. (Can't say the same about the service provider though).

Found an issue where it doesn't work with block caching. Which might not be something easily fixable in D6. I got arround this by doing the following:

function my_module_init() {
  // Initialize Ad regions based on which blocks are visible.
  // This is so that even if block caching is enabled, the header script tag pulls in the correct regions.
  if (function_exists('_openadstream_positions')) {
    foreach (_openadstream_positions() as $position) {

      // Insert logic here to determine a block's visibility goes here.

      if ($visible_blocks[$position['name']]) {
        openadstream_positions($position['name']);
      }
    }
  }

}

The slight drawback to this method is that if you arrive on a page where blocks haven't been cached yet, openadstream_positions() will record those positions twice. Not sure if this will actually double the ad view stats, but better safe than sorry. This patch fixes that.