The very minute the iOS 4 software was made available for iPhone 3G/3GS owners, I updated mine at once. I did not encounter any issues on installing the new software. It was simple. It only took me about 20 minutes to finish the entire process.

It was on the third day when I noticed that my Facebook App wasn't working 100%. I could still check my friends' updates, photos, read messages, accept friend requests BUT updating my status and commenting on my friends' shouts ~~~ totally disappointing. After pressing the "share" button, the entire app just froze. Such a nightmare! I was so near to uninstalling the iOS 4 software! Grrr....

Anyway, if you are having the same problem [Facebook App just hangs when logging in or updating your status, etc.] try to uninstall the app and reinstall it back again. This has worked for me. It will probably work for you, too!