Yes. If you watch sports, it's worth getting just for the fact that you can pause, rewind, and slow-motion live TV... instant instant replay.
Remember that you have a fee of about $10 a month, or you can pay by the year I believe. I haven't looked at cc bill recently, but when I first got mine a few years ago, it was $9.99 a month. I'm pretty sure it has increased since then.
check out
http://www.tivocommunity.com
editted to add that you should go with either a Philips or Sony TiVo. I have a Philips, my friend has a Sony... but they are pretty much the same. The Sony looks cooler though
And if you know your way around a computer (hardware and such) you can easily buy a lower end unit, that is one with a lower recording capacity (mine was a 14 hour unit... may not be able to find them anymore except for on Ebay) and you can add another hard drive to it and increse it's capacity. Mine now holds up to 80 hours of video.