What is the life span of the H1N1 virus outside the host?
The H1N1 is very simliar to other viruses and batcteria. It can survive about two hours (or a little longer, depending on the type of surface) when it is outside of a human host. Sunlight is another factor...the virus does not do too well when exposed to sunlight or high temperatures (hence the reason the body goes into a "fever" when sick.)
It doesn't seem like that's very long, and it might not be in your house (where you can control how many people come in contact with your stuff) but imagine the situation at a mall, or a 24 hour gas station. So many people go in and out, coughing, sneezing, and touching stuff that there is a fairly constant "deposit" of fresh viruses for others to catch.
Sick people, also, keep churning them out. The kicker is that the virus is multiplying in sick people before they even show any symptoms, so it is possible to get sick from someone who looks perfectly healthy. Your best bet is to keep your hands clean, limit your interaction with large groups of people, and make your plans ahead of time for how to cope (work, kids, etc) if you should become sick. At the rate this particular flu spreading, we'll all be lucky if we're not "knocked out" by it at some point!