=======================================================
The code below works (it's the code from 1.6):
=======================================================
 * @package BuddyPress Core
 */
function bp_core_get_users( $args = '' ) {

	$defaults = array(
		'type'            => 'active', // active, newest, alphabetical, random or popular
		'user_id'         => false,    // Pass a user_id to limit to only friend connections for this user
		'exclude'         => false,    // Users to exclude from results
		'search_terms'    => false,    // Limit to users that match these search terms
		'meta_key'        => false,    // Limit to users who have this piece of usermeta
		'meta_value'      => false,    // With meta_key, limit to users where usermeta matches this value

		'include'         => false,    // Pass comma separated list of user_ids to limit to only these users
		'per_page'        => 20,       // The number of results to return per page
		'page'            => 1,        // The page to return if limiting per page
		'populate_extras' => true,     // Fetch the last active, where the user is a friend, total friend count, latest update
	);

	$params = wp_parse_args( $args, $defaults );
	extract( $params, EXTR_SKIP );

	return apply_filters( 'bp_core_get_users', BP_Core_User::get_users( $type, $per_page, $page, $user_id, $include, $search_terms, $populate_extras, $exclude, $meta_key, $meta_value ), $params );

=======================================================
This one doesn't work (it's the code from 1.7):
=======================================================

 * @package BuddyPress Core
 */
function bp_core_get_users( $args = '' ) {

	// Parse the user query arguments
	$params = wp_parse_args( $args, array(
		'type'            => 'active',     // active, newest, alphabetical, random or popular
		'user_id'         => false,        // Pass a user_id to limit to only friend connections for this user
		'exclude'         => false,        // Users to exclude from results
		'search_terms'    => false,        // Limit to users that match these search terms
		'meta_key'        => false,        // Limit to users who have this piece of usermeta
		'meta_value'      => false,        // With meta_key, limit to users where usermeta matches this value
		'include'         => false,        // Pass comma separated list of user_ids to limit to only these users
		'per_page'        => 20,           // The number of results to return per page
		'page'            => 1,            // The page to return if limiting per page
		'populate_extras' => true,         // Fetch the last active, where the user is a friend, total friend count, latest update
		'count_total'     => 'count_query' // What kind of total user count to do, if any. 'count_query', 'sql_calc_found_rows', or false
	) );

	// For legacy users. Use of BP_Core_User::get_users() is deprecated.
	if ( apply_filters( 'bp_use_legacy_user_query', false, __FUNCTION__, $params ) ) {
		extract( $params, EXTR_SKIP );
		$retval = BP_Core_User::get_users( $type, $per_page, $page, $user_id, $include, $search_terms, $populate_extras, $exclude, $meta_key, $meta_value );

	// Default behavior as of BuddyPress 1.7
	} else {

		// Get users like we were asked to do...
		$users = new BP_User_Query( $params );

		// ...but reformat the results to match bp_core_get_users() behavior.
		$retval = array(
			'users' => array_values( $users->results ),
			'total' => $users->total_users
		);
	}

	return apply_filters( 'bp_core_get_users', $retval, $params );