The key feature of the Zune music service, so far, has been the "Zune Music Pass," a DRM-protected music subscription service which allows users to download and stream as much music as they like for as long as they maintain their monthly subscription, so that users can enjoy their music at home or at work, on PCs, phones, Xboxes or Zune players.
In the US, subscribers are also offered ten DRM-free songs per month, which can be retained even if the subscription is cancelled.
However, Starting September 13, Zune users in Europe will see a reduce number of devices to which Zune Music Pass content can be downloaded, from the current level of six (3 PCs and 3 Windows Phones) to just four (at least one PC, plus any combination of 3 PCs or Windows Phones).
According to the email sent out today to European users states, "subscribers' continued use of Zune Music Pass beyond 13 September will implicitly confirm their agreement to the new arrangements."
The email doesn't have 'any reason or any mention of Zune hardware,' so it may be that these changes do not affect users in the US or Canada. In the US, Zune Pass remains available for up to 3 computers and up to 3 devices.
Per Zune.net website:
You can download and sync music from Zune Pass to three computers and three devices (Zune players and/or Zune-enabled phones). Once you've put music you've downloaded with your Zune Pass on a computer or device, it is associated with your Zune Pass. If you want to change the computers or devices that are associated with your Zune Pass, you can swap out one computer and one device every 30 days.