PushMail [$4.99 - iTunes link] takes a different approach to working around the lack of push notifications for Gmail, Hotmail, and other email services on the iPhone. When you set up PushMail, you're prompted to create an account on their servers ([username]@dopushmail.com). You then forward email from Gmail, Hotmail, etc. to that PushMail account (using whatever filters or rules you like), and when PushMail gets the forward, it sends a push notification to your iPhone, alerting you that your Gmail, Hotmail, etc. account has email.
You can also forward more than one account to the Pushmail account.
If you give it a try, let us know how it works for you.