Update: Go get it now (be sure to click where they tell you to).
Ah, the best thing about waiting for carriers to offer ROM updates isn't the actual official release, it's the leaking that happens beforehand. As Jimmie says below, it probably makes sense to just wait a bit as the official update is expected this week. But if you're not that sort, a bit of Googling should net you the update pretty quickly. In the meantime, you can check out them pretty WM6 screenshots.
Update: Gizmodo confirms that it's coming out for really real on Friday.
T-Mobile is expected to offer the Windows Mobile 6 upgrade to current Dash owners next week for download. It has been leaked on the usual sites known for obtaining these upgrades (I'm not going to list the sites). You're better off waiting for T-Mobile to officially post it for download, it is expected to be made available this week as a download for current Dash owners