The tweet, which was later removed, said that "Mac users would be able to use Zune on their Macs to sync with #WP7." This is a noteworthy move, as Microsoft has been stalwart in their efforts to keep Zune within the Microsoft family.
Many have speculated that Mac users would have to use a basic Zune-esque client to sync their devices, but a full Zune application is obviously more appealing. The adaptation of Zune for Macs is more likely a focused effort for Windows Phone 7, rather than a knock on Apple's front door. It is no more invasive than iTunes being available on both platforms.
The expansion to Apple computers is unsurprising when viewed in the context of recent events. First, Microsoft has released Zune for all the countries in which Windows Phone 7 will be available. Second, they are offering a 3-month Zune Pass to new Zune subscribers. This would be particularly appealing to previously Apple-only users cheating on Steve Jobs with WP7.
The removal of the tweet might be indicative of its authenticity. Microsoft might have wanted to keep that fact under their hat until a later date, or perhaps they are merely considering the idea of adapting Zune for Macs.
source: Neowin via wpcentral