Checking out your twitter rank and authority is a great way way to kill time !
Apart from that ranking and grading of your account helps you get intresting facts about your tweeting habit along with providing you opportunity to check as to how you rank among twitter users worldwide. Twitter ranking also makes twitter more nriching along with providing you some really cool statistics and also helps you be a better twitizen. Twitter ranking mainly depends on frequency of your tweets and your follower following ratio, influence and authority of people following you, and the number of retweets you get. There are many third party twitter ranking tools available today.

Some very popular twitter ranking tools include:

Twitterholic
Twitter Grader
Tweetstats
Twitterrank
klout