Well, originally, tinyurl just went for sequential short URLs too. But as those were predictable, abuse was afoot: "Early on, the resulting URL aliases of the service were predictable, and were exploited by users to create vulgar associations. The URL aliases dick and cunt were made to redirect to the White House websites of U.S. Vice President Dick Cheney and Second Lady Lynne Cheney." Source: http://en.wikipedia.org/wiki/Tinyurl#Early_abuses