Yes, TMN shows some Showtime programming that HBO does not. However, I would guess that 99% of viewers in the U.S. that get HBO also get Showtime. So if you're not too lazy to change the channel, you can still watch Dexter or Californication (or Weeds, which was absolutely fantastic until it got really serious and strange this year).
Also, some people are talking about $40 to $60 a month for the movie channels. I'm not sure where they're getting their figures, but the DirecTV Premier package is $104.99 a month for every channel except the pay-per-view channels or any sports packages. That's for 265 channels and quite comparable to what I pay Cogeco (for far fewer channels). Throw in $5.99/mo for the DVR fee and $9.99 for HD Access with 50+ HD channels (DirecTV touts 95 but a lot of those are regional sports channels showing the same programming on up to 30 different channels). You can even program your DVR to record from the web or your BlackBerry!
The only gain I perceive through Cogeco is with the Super Sports Pack. At $30 a month for NFL, NHL, MLB, NBA, NASCAR, OHL, and NCAA Football & Basketball programming, it's a steal at only $360 a year (and I usually cancel for a couple months in the summer). NFL Sunday Ticket alone costs $259 through DirecTV, which is the exclusive provider in the U.S. The SuperFan package to add more HD games as well as the RedZone channel and the condensed games throughout the week is another $99. Combined, that's the total cost for the Super Sports Pack through Cogeco.
Also, I'm guessing those of you arguing about MTV Canada not showing music videos haven't seen MTV in the U.S. for 15 or 20 years. MTV in the U.S. doesn't show videos either! Neither does VH1. These aren't music channels anymore, they're reality show / pop culture channels now.