Sezmi looks interesting, but I notice that Premium cable channels (HBO, Showtime, etc.)are not available, and they carry only 23 cable channels. For example, FX and AMC are notably missing from their line-up. And it looks like all On-Demand programming would include an additional pay-per-view fee. Except for new theatrical movies and a few big-ticket sporting events, all On Demand programs are now free with Comcast.
So given my viewing habits - mostly cable channels, some HBO, and a lot of On-Demand - I'd probably end up paying as much or more per month for Sezmi than I do for Comcast.
It's worth keeping an eye on though -their line-up could improve.