Yammer’s biggest rule of thumb is “2 to 10 people, 2 to 10 weeks,” which means they generally don’t do projects that are larger or more complicated. There is a non-linear relationship between the complexity of a project and the wrap-up integration phase at the end. If you go anywhere beyond ten weeks, the percentage of time in the wrap-up phase becomes disproportionate.
If you employ the “2 to 10″ rule, it’ll also force you to release often, test your assumptions, and not over-invest in mistakes. It’s sort of the lean startup mentality, and if you’re going to try and do that you have to codify it in your organization.
Sounds like half-assed Agile – and as such might work well in a surprisingly big number of organizations.