There is a thread currently running on the php internals mailing list about
finally dropping support for php4! It's about time! Reasons given are to force the hand of hosting providers and application developers to finally upgrade to php5. I couldn't agree more, bring it on! PHP5 has been out for years and unlike some of the crap you read it's been quite stable and the performance is good. There's no excuse not to update.
GoPHP5 is a great initiative promoting the uptake of php5. They outline the reasoning behind why you should update. They list php5 software and hosting providers that support php5. I say if your hosting provider doesn't offer php5, get a better web host!
Good riddance PHP4!