I love my gmail account and these features sound exciting: The address book import/export is a biggie to me. I'd like to see support for Mac OS X Address Book, ideally i'd like to be able to sync stuff back and forth, but I'm not sure how much sense this would make for a web-only mail system. Yahoo mail doesn't support syncing, unless you purchase Intellisync.
A nifty feature of EarthLink's Total Access for Mac OS X is that it allows me to sync the OS X Address Book with their online address book, which ties into their mail system. EarthLink's highest-level spam protection setting partly relies on white-listing various email addresses: People who send you an email for the first time are offered a simple procedure to request from you to be added to your white list. Upon your acceptance, they're automatically entered in your earthlink online address book. Whenever you select the "Sync Address Books" feature in Total Access, all contacts stored in your OS X Address Book are now part of your earthlink address book, which means they are all on your "white-list". Conversely, all contacts that were added to your online address book by the earthlink mail system now become part of your OS X Address Book.
Regardless, being able to import contacts into gmail would already be a great feature. GO GMAIL!