In my experience, Android does a poor job with modal dialogs (i.e. pop-up windows). In particular:

• Modal dialogs are destroyed when the screen orientation changes.
• On higher resolution devices, modal dialogs tend to not take advantage of the larger amount of screen real-estate. This often leads to frustrating and awkward user interfaces, especially with text.

Consequently, I recently updated Vault 3 for Android by replacing most modal dialogs with full screen "Activities".