Don't create multiple annotations with the same simple name

Nobody reads imports. Good IDEs do their best to pretend imports don't even exist - they'll hide 'em from you, and manage them for you. They'll even add imports on demand when you're writing new code.

Suppose you create your own, say @Inject or @RequestScoped annotation. In the code, it's practically impossible to differentiate between this and a Guice-supplied annotation:

package com.publicobject.pizza;

import com.google.common.base.Preconditions;
import com.google.common.collect.ImmutableSet;
import com.google.inject.Injector;
import com.google.inject.Provider;
import com.publicobject.pizza.annotation.RequestScoped;
import com.publicobject.pizza.annotation.Inject;
import com.publicobject.pizza.geography.GeographyService;
import com.publicobject.pizza.hr.EmployeeRoster;

@RequestScoped
public class PizzaStore {
  @Inject PizzaStore(GeographyService geography,
      EmployeeRoster workers) { ... }
}

Your head will explode debugging problems if the wrong annotation is applied. Guice can detect some problems (blowing up on a mismatched scope annotation) but it's still risky business.