I love using PHP 5 to do stuff, because it feels much more like writing in a real language than PHP 4 did. The expanded error message text when runtime errors occur is so much better than the stuff in PHP 4. I also like a handful of the new functions (file_get_contents() and file_put_contents() since i'm lazy as hell at times), as well as the expanded OOP implementation, despite the few steps taken away from the standards we see in C++ and Java (constructors not named for the class anymore...). Granted, I'm partial to much more powerful OO programming due to my background in C++ (i want function overloading , but we'd need types for it). I'm excited to hear of PHP 6, perhaps things will get even better.
I've developed a number of things using PHP 5-compliant code, however I haven't really taken full advantage of it except for in my latest endeavour, a crazy idea that I won't go into here...
More on topic, I blame hosts for the slow switch. Since the release of PHP 5.1, I judge it to be quite stable (i've been running since 5.0.3 i think, on windows with apache 2, all of which sounds like it should be crashing every 10 seconds) because I've had no issues whatsoever. Hosts should know how to administer their servers better than the average linux enthusiast, because they're getting money to do it. I set up php 5/apache 2/mysql 4 on linux for my school in an hour, and i don't consider myself to be much of a linux master.
For the most part, PHP 5 will run valid PHP 4 code (just some issues with MySQL if it isn't set up correctly), so I don't see how there is any problem with that sort of a transition--nothing needs to be recoded. I agree with everyone who said that the hosts should get off their butts and fix it--we're paying them to do it, they should serve us how we want to be served (within reason, and i don't see supporting php5 instead of 4 as too demanding).