Personally I'm all for earth day, or rather earth day, every day and I am a Christian. (As a matter of fact I am a big organic person too- I try to grow my own food as does my family) I don't see anything wrong with taking care of the beautiful world around me. Plus, taking of care of the earth benefits not just the earth but everyone else- it's using what we have wisely, how exactly is that wrong. And just for the record, I'm not concerned about the rapture (I'll probably be dead before it ever happens). I am concerned with living my life today.
Earth Day is part of the environmental/green movement which ultimately is a worship of nature. Christians should have nothing to do with this. That is not to say we should not try to be good stewards, but the environmental movement is ultimately anti-christ.