Just FYI: I exchanged my 3100HD for a 3250HD at the Raleigh office today. Little more info about the 3250HD. Under settings and then "More Settings" there is a setting for Aspect Ratio where you can set the ratio for your TV and then whether or not you want sidebars, zooming, or stretching for 4:3 programming. One note though... on HD channels, if there is 4:3 programming, this setting does not come into effect and there are black sidebars instead of the grey ones that the 3250HD normally superimposes for 4:3 programming.
Also... I have a DVI port but no way to check whether or not it is active. And, very strangely, the VOD channels, although flagged by the box as 4:3 programming, do not stretch/zoom when in those modes. They simply come up with grey sidebars.
Edit: One other neat little thing. On the 3100HD the digital audio output would go dead on the traditionally analog channels (e.g. 0-77). On the 3250HD the only channel that appears to have no audio on the digital audio output is 218 (NBC-SD).