The longest streak of Up years is 9 (1991 - 1999).
The longest streak of Dn years is 4 (1929 - 1932).
The current streak (as of Dec '14) is the second longest (6 years).
Before that, there were two streaks of 5 Up years, one of which ended with the market crash in 1929. The crash of '87 happened in the middle of the second 5 Up year streak (1985 - 1989).
The average (excluding years when the DJIA changed direction immediately after 1 year) is 3.25 for Up years, and 2.33 for Dn years.
Long Up streaks don't necessarily get followed immediately by long Dn streaks.
For the last 130 years the ratio of Up to Dn years is close to 2:1.