I think a lot of the tanking these days can be credited to San Antonio in the NBA. They were a good team for a long while with David Robinson who they got in 1989 and they were a contender up until 1996 when he got hurt for a season.
They sucked fiercely that one year and ended up with the first pick (won a lottery, they were the 2nd worst team I believe) and got Tim Duncan. They immediately rebounded and won some championships.
If you look at their record by season, you can see how much of an anomaly that season was and it basically has given them a 25 year run as a contender -
http://en.wikipedia.org/wiki/List_of..._Spurs_seasons