Originally Posted by Tom Scott 
It won't be true push email - you cannot have "push email" setup without some kind of server at the backend doing the pushing.
It'll simply launch an IMAP connection to the server and use the IDLE extension to monitor for new mail - so you'll have an "always on" connection to the server. Also not all servers support IDLE extension
Get a BlackBerry if you want true push email.
Thats exactly how it works
Push email in a sense though. Similar enough for SE to label it 'Push Email' in their menu.