It was my understanding that one of facebook's most recent app updates was the enabling of video uploading. I could be wrong so dont hold me to it but last time i checked, you go into news feed then click on the camera icon next to where you input your status and choose pic/video upload (should be same button for both).
I should have double checked before replying but w/e, ill double check now.
UPDATE: i was semi correct. The button is labled "choose from library" and yes you can upload iphone 4 videos. And yes i just took a five second video of my room in the dark and posted it on facebook for everyone to question my sanity. Youre welcome.