Google Sync had support for synchronizing both contacts and calendar events over ActiveSync for quite a while now. Finally support is extended to e-mail account.
Instead of IMAP account that gets "pulled" for updates every X minutes, real "push" e-mail is supported. This both speeds up process of getting actual e-mails and decreases cost since TCP/IP traffic is almost non-existent when there is no new e-mail waiting.
Whole thing integrates perfectly into Windows Mobile as direct replacement for Exchange Server and only thing still missing is support for tasks. I am sure that this is coming sometime in the future.