Today I'd like to provide you with a little commerce.module snippet to determine the currently selected product variation (using commerce_product_reference.module) of a product display with several variations.
I had to search hard for it so here's the code for you:
// Determine the currently selected product or default product for this product display
$node_wrapper = entity_metadata_wrapper('node', $product_display_node);
$products = $node_wrapper->field_produkt->value();
$current_product = commerce_product_reference_default_product($products);