In order to take advantage of the changes in Drupal 7, Views has gone through several API changes. +Here's what you should know.

Handler registry

Views now uses Drupal's dynamic-loading code registry. You can safely remove your implementations of hook_views_handlers(), since they are no longer used. Please remember to specify the handlers in your module's .info file. For example:

name = Example module
description = "Gives an example of a module."
core = 7.x
files[] = example.module
files[] = example.install

; Views handlers
files[] = includes/views/handlers/example_handler_argument_string.inc