i use zass. have 256mb ram.
my vsmon shows 16,196 K in the taskmanager.
u r right about one thing though, the earlier vsmon's use to take lesser resources. there is /was talk about this in the zonelabs forum too, on this subject.
another thing za f/w or zass doz take time to load and unload. this is probably bcoz, unlike others, it even loads/unloads its service completely; and not just its processes.
thats y i prefer to use zass. i unload it (completely) with a click, when not on the net, and load it only ven on the net. with its triple defense system (firewall/antivirus/antispy) i have found it very effective.