That's right...nothing in '06. HBO is unique in that it allows shows to be produced on a schedule of their choice.
Larry David takes his time to produce quality shows and doesn't have to worry about meeting a pre-determined schedule, as is the case in network television.
There was 18 months between seasons 4 and 5, so this is not a surprise. Also, Larry wasn't sure whether there was even going to be a season 6. That decision was just made a couple months ago.