It doesn't support two different lineups when using the built-in tuners as far as I know. It uses only a single coax connection so that means only a single cable source. You can also connect one external input (external cable box, sat box or vcr etc..)
Once you've used two tuners you'll wonder how you lived without it. I could never have truly enjoyed a single tuner TiVo. Two tuners is about 10 times more useful than 1. The benefit drops off significantly after 2 though.
It's a shame the box can't control nor record two external inputs. This would not have cost them much to add, considering the bulk of the cost would likely be the MPEG encoder chips (which it already has a pair of).
TiVo teased me earlier in the year with official data support for Canada and now finally dual tuner stand-alone. But even if the single external source was not a deal breaker, their subscription service is. I won't pay a monthly fee. A PVR is a product, it is NOT a service.
Guide data costs real money, but they need to think of a better business model if they want to capture significant market share. This is especially hurtful when you're essentially paying twice for the same thing (Digital cable already pipes guide data).
Bruno