I don't see why any application should require register_globals to be on. We have $_GET for things like that. Coding applications using register_globals seriously deteriates the code-readability, especially for third-party developers.

Although I always disable register_globals, I also properly initialize my variables. If you code with full error reporting (notices, etc) this is very easy to achieve as PHP will warn you about those uninitialized variables. Doing this enables you to run your code on servers with register_globals on or off, while either not properly initializing your variables, or requiring register_globals to be on, seriously limits your code's compatibility with different servers.