I have been using the Gmail mobile application since long.It has been very useful to me. whenever any new mail come it shows notification on the screen. Earlier I had to check it by opening the mailbox. It has also provided the feature of sync which can be enabled or disabled. the only dofference is if u click on sync it will automatically sync your local mailbox to the server and retrieve all the mails otherwise it need to be synced by scrolling the screen. It also allows to add more than 1 account.
Good one.