I don't mind it, since CTV seems to end Lost a couple minutes before 9, while ABC has it run right to the top of the hour. So, by the time CTV has shown it's preview, they've already switched the CTV feed off of my ABC affiliate (since no one shows Alias at 9), so I can the ABC preview, too.
And, for whatever reason, my cable company doesn't bother to do it with CH, so I can watch the previews for the next week's episode of 24 after the show, too, which CH doesn't show at all.