HUD-mandated homeless counts are currently the best method available for communities to quantify numbers of homeless individuals and families at a given point in time, but thankfully that hasn't stopped communities from attempting to improve upon this method.
One example of such an effort is the 100,000 Homes Campaign (http://100khomes.org/). They are working with their local community partners nationwide to integrate innovations such as their Registry Week and the Vulnerability Index into local homeless counts to help communities move beyond quantifying to also building relationships and assessing the needs of their homeless neighbors.
Also, as communities count homeless people, this piece by Bill Gates on the importance of measurement is very timely. http://online.wsj.com/article/SB1000142412788732353980457826178064828577...
Let's share and discuss best practices and information, so we may continue improving how we measure the extent and severity of homelessness, and thereby accelerate the replication and scaling of what works.