WP 3.1 getting tax_query to work in query_posts()

$todaysDate needs to be an array of two values to be BETWEEN for the compare.

For example if you wanted to use a date range from today to a week in the future, then you might use something like..

$todaysDate = array(
    date('Y/m/d'),
    date('Y/m/d', strtotime('+1 week') )
);

Or if you wanted to go back in time, then maybe..

$todaysDate = array(
    date('Y/m/d'),
    date('Y/m/d', strtotime('-1 week') )
);

Following on from the comments: try this as the meta_query part of your code.

'meta_query' => array(
    array(
        'key' => 'StartEventDate',
        'value' => date('Y/m/d'),
        'type' => 'DATE',
        'compare' => '>=' // more than or equals
    )
)

NOTE: It’s still possible to use the old >(more than), <(less than) and other meta comparisons with the new meta_query args, or at least it looks that way by looking directly at the source.

http://core.trac.wordpress.org/browser/trunk/wp-includes/meta.php#L355

Hope that helps.