Personally, I'm really excited for it.
In the Apple iPhone activation video, during the part about syncing stuff over through iTunes, there was a button/checkbox to allow you to sync your Yahoo! Mail contacts. I'm pretty sure that would require you to enter in your Yahoo! Mail ID and password, which would then (possibly; this is just conjecture) automatically set up, if you want (perhaps there would be another checkbox or whatever), push e-mail for your Yahoo! Mail account.