Suppose you have just moved your blog to a new webhost and want to check whether DNS changes are globally propagated so that the blog domain resolves to new webhost consistently from different parts of the world.
Whatsmydns is an online tool that checks for this info from various parts of the world and displays the results.
Simply go to Whatsmydns and enter your blog address, select the DNS records for which you need information (A, MX, CNAME etc) and hit Search.
Pretty nice and graphical way to find out DNS information.