OK, then what we do if something weird happens in production and we want to see the errors, but we don't want others to see them? [...] Maybe PHP could have some setting like display_errors=local which would enable display_errors for requests originating from developer machine but would disable it when outsider accesses it?

Richard's solution checks the HTTP_HOST value of the current request and, based on whether it's marked as "live" or "dev", uses a ini_set to change the display_errors setting to true/false.

I've not added any new features to the class; I've simply updated it to be, well, better. Plus it uses PHP5's object model better. It's really just an update, ie if you're using the old version and it works, then you have no real reason to update it.

You can check out the source here and an example of it in action here.