Looks like Tivo is quietly rolling 8.3 out to a few select customers.
If you want it faster, sign up for the priority list.
Series3 units will have an update soon, followed by a full rollout.

The when it happens, your Tivo will have a Build Message that should say:
We just upgraded your Tivo service with the Spring 2007 Service update. This update includes more options for programs in your Now Playing list and integrates support for TivoCast content. For more on what is in store with this update… More Options
When viewing the program screen for any recording, you’ll now notice a “More Options” menu item. From here you’ll be able to schedule additional recordings including the option “Get a Season Pass”.
Tivocast
You’ll now see logos for TivoCast partners making it easy for you to ID the source of your broadband video at a glance.
Tivo Desktop
If you’re trying the TiVo Desktop 2.4 for Windows Preview Release, there is a feedback forum here.
Phone Connection
Also, if you’re still using a phone line with your TiVo (you really want to use broadband if you can), it looks like the pool of available numbers shrank on March 1st. You may need to change the dial-in number your TiVo is using if it has had problems connecting.
2006 Engagdet Awards
And don’t forget to vote for TiVo. Currently in second place, after the Slingbox Pro.

Thanks also to Zatz Not Funny who has a post on this.