Rated 5 out of 5 stars
This add-on is very useful, I use it with Growl for Windows and Prowl client for the iphone.
I setup my two Gmail accounts so that they get pushed to Thunderbird using the Idle Imap trick and then Growl pushes it to my iphone. It takes about 10 seconds for an email to pop up on my iphone.
I also added an RSS feed to my Twitter feeds and those get pushed as well.