Unfortunately, it's now $300 for the lifetime guide data. I wish I hadn't waited and had bought it for $250. Lifetime guide data refers to the lifetime of the Tivo unit, not the person with the subscription, so the lifetime subscription is not transferrable to a new unit should you decide to buy a new one. The lifetime subscription is tied into the unit's serial number. The serial number is hard-coded into the unit's ROM, so if you just need to replace the HD, you do not lose the subscription.
Many VCRs only allow you to program 8 items at one time. I've had over 46 "season passes" programmed at once, and I'm sure it could go higher.
Another advantage over a VCR: Say you come home at 7:20, and you've programmed the Tivo to record an hour long show that starts at 7:00. You can sit down and watch the beginning of the show right away, while the Tivo multi-tasks for you and records the rest. With a VCR, you would need to wait until 8:00 before you could rewind the tape to watch the show from the beginning.
Capacity and Expandability: With your computer, a downloaded linux program burned to a boot CD, and instructions from the web, you can make almost any IDE drive into a Tivo drive. You can fit up to two IDE drives inside your Tivo. At basic quality, 1 GB = approximately 1 hour of record time. If you use medium quality you'll get a much, much better picture, and 1 GB = approximately 40 minutes. There are also "high quality" and "best quality" recording modes, but for normal time shifting usage, I don't see much call for using them.
Disadvantages: The HD is always spinning, and therefore, it's prone to periodic failure. It's pretty expensive. It needs either a phone line or a broadband (Series 2 or Series 1 with network card) connection to make its daily call for guide data. It's always on, using electricity (I haven't tested it, but my series one says 1 amp on the back, that's more than a 100 watt light bulb).