Aside from the various points being made in the comments section, it seems folks have overlooked a very serious reason that apartheid should be the term used with regard to Israel:
1) Apartheid is defined by the international community and Israel's policies/system fall within that definition.
2) Apartheid, is defined as a crime against humanity under international law, and is therefore prosecutable under international law.
Good point. Israel supporters' response to the Goldstone report shows that there is real fear of actual accountability. But does it have to be either/or? Both terms seem to help people best understand what's happening in Israel/Palestine.