I tend to lean towards the "better to be prepared" mentality, if for no other reason than I often end up in ridiculously improbable backcountry situations. I'm thinking either a 9x10 or a 10x11. I might even try to score some Tyvek, as there are a lot of construction sites on my way to work. Maybe if I turn on the charm I can get some for free, haha!
@Brian: I've always had my eye on that tarp, maybe using it for hammocking will finally make me "pull the trigger"!