In my view most of us are focused so much on completion of the project that documenting lessons learned looses out on its priority. In our mind we have learnt the lessons so further documentation is given a skip. Having said that I think if we make "lessons Learned " a milestone in a project and a mandate for a formal sign off we may see some results. Initially this may be a push method but nonethe less if we can start capturing its benefits then there will be a cultural shift in the mindset.