Jon,
There are those who shy away from hammerbeams because of the characteristic of outward thrust exhibitied by a badly designed/constructed trusses. My personal view says there is no more attractive configuration. Check out the Russell Colbath project in NH here on the TFG website for views of a big hammerbeam barn/educational facility. The design geometry which puts all the thrust downward avoids the outward movement problem. Notice how a flying buttress effect can be achieved which further contains the hammerbeam.
