I have found by trial and error that components of the HP printer driver were causing or contributing to a problem with my Mac Powerbook going to sleep. If I open up the Activity monitor and force quit all processes with HP in the name... The sleep function seems to work normally. The problem stays quiet until I use the driver again, then regardless of restarts, forced sleep, etc. the driver stays active until I go back into the Activity monitor and force quit.. An unwieldy solution at best.
Are there preferences in the driver that I'm missing that would help with this issue?