Curious About Indoor Air Quality?

Ricky Ng-Adam asks: "The Science Advisory Board of the EPA has 'consistently ranked indoor air pollution among the top five environmental risks to public health'. As most of you are probably spending most of your time indoors like myself, I'd like to know how this affects you and what do you do to deal with it? Is it worth it to buy an air purifier and if so which one?" Also, how well do purifiers deal with common indoor air polution, like smoking...and pet hair/dander (for those of you who spend lots of time working at home)?