TiVo is the most well-known "Personal Video Recorder" (PVR). It "knows" when television shows are going to be on, and can record them for you according to a variety of conditions you can give it. Since it records to a hard drive, you can then later watch these shows however you wish, whenever you wish, jumping around them, fast forwarding, rewinding, or skipping back with impunity. It also provides the same services for up to 30 minutes of Live TV. I highly recommend owning one if you like TV at all, or if you "don't like TV" but find that you sometimes like certain programs either. (I don't know that there are very many people who "like TV" as in "liking the vast majority of programs they see"; I'd suspect nearly all of us only like single-digit percentages at best.)
The television industry has mixed opinions about the whole thing; on the one hand it vastly increases the value of their offering with no particular effort on their part. On the other hand it allows consumers to skip commercials, and it seems some television executives believed that there was an unbreakable contract between the television producers and consumers that the consumers must watch the commercials. Apparently these executives don't watch TV much themselves, or they'd know about the invention of the Mute Button, along with Channel Surfing, Using the Bathroom, Getting a Snack, and of course just plain Ignoring the Commercials, along with the wide variety of other ways people have found to not watch commercials on television.
Interestingly, and perhaps to the television executive's chagrin, none of this message integrity analysis affects TiVo. TiVo is just a tool that does as you say, it contains very little content of its own (and that content is correctly independent of the television shows). Skipping around and such under control of the user are perfectly valid uses of the message. While television executives may prefer that you watch a television program straight through, they really have no grounds to make that demand.
If TiVo tried to send a programmed sequence of commands to your machine so that you could, say, skip over commercials automatically, that would be over the line, because that would be sending a patch to remove commercials from the television show using a TiVo, patches very dependent on the exact show being shown. The current TiVo is fine, though, and is just another example of how the receiver will continue to be empowered by technology.
ReplayTV provides a great borderline case. ReplayTV is another PVR, one that tried to ship just such an automatic commercial skipping algorithm. This automated commercial skip, which is also a feature in at least some VCRs (my parents have one) is technically not accomplished by sending patches through to the user, especially in the case of the VCR which is not connected to anything. In the end, though, it's equivalent to such a patch and is basically a smart filter, and is probably a textbook case of being just barely over the line. As such, it was ethically correct to "a href="http://www.wired.com/news/business/0,1367,58957,00.html">remove it from the product. (Though that does bring up the question of how ethical it is to remove a paid-for feature from a product after the owner buys it.)