At first blush, Google Analytics only provides statistics for previous dates, as the main statistics graph does not extend into the current date.  You can use Analytics to get statistics for the current day, however.  Simply click on the date at the top right of the graph, and select the current date as both the start date and end date, and Analytics will provide you with statistics for the current date.  Given that different traffic monitoring applications may not measure visitors, page visits, and others statistics in the same manner, there is no way to know for sure that the stats are 100% accurate, but I've compared the visitor count with the real-time count on my site from Clicky, and the two are typically very close, and sometimes identical.