COMCAST had a working demo at CES. However, the core hardware used by COMCAST is so limiting the use of the device, regardless of the GUI, will be less than a full experience.
I would vote to hold onto the Moto since you already have it, and then you can judge once the new software is loaded (at a small additional fee per month, I have read).
The S3 is my choice, however. Using the Amazon.com "Unbox" to download movies to the unit replaces the on-demand for our uses. It's not an exact replacement, but it comes close. Seeing what is recording on the two tuners on the front panel, having built in Ethernet, being able to program recordings via the web when not at home, etc, etc.
Hang in there. Meanwhile, the Guide information is now appearing for the four new HD channels. Sweet. Took a little over a week after filling out the form at the Tivo site.