I've had my Droid X for almost a month now and I have yet to find out how to get my Gmail to sync and notify me that a message has arrived without going in and manually refreshing my Gmail account. Can anyone help me?
I have gone into settings in Gmail and changed the Duration and Labels to try and sync it and notify me but that hasn't worked either 
Here are the steps for syncing your Gmail. Hope this helps!
- From the home screen, touch the applications tab (located at the bottom of the display).
- Touch Gmail.
- Press the Menu button.
- Touch Accounts.
- Press the Menu button.
- Touch Account settings.
- Touch Background data to enable applications to sync, send and receive data at any time.
Enabled when a green check mark is present.
- Touch Auto-sync to enable data to sync automatically. Enabled when a green check mark is present.
- Touch an account.
- Touch any of the following Data & synchronization options: Enabled when a green check mark is present. Repeat steps 9 and 10 as necessary to configure additional accounts.
- Sync Calendar
- Sync Contacts
- Sync Gmail
