My LSAT (Law School Admissions Test) teacher told us that some means "at least one" and that it could mean up to all of the group. I don't know if this only applies to the test or to grammer in general, but I thought I'd throw it out there for consideration.
When I hear the word "some" in everyday conversation I usually think that it means a significant number of the group, probably not more than half. I don't know what that's worth, but I thought I'd throw that out there too.
~Anna
