Yes, you do want 4 tuners in a TiVo!
Last month, I bought the unit just below this one, basically same box, but with 1/2 the drive space and only 2 tuners. I just now got into TiVo because they finally signed agreements with Cox Communications, who is my cable provider, to carry all the digital channels via Cox's cable card setup. The TiVo setup was easy, but Cox took 3 days to get their card working properly. Cox really needs to train their folks better... :/
First thing I noticed that I was getting more digital channels than with Cox's own digital tuner. Odd, eh? No matter, it's all good. I'm no longer paying for their eqiupment, and I payed the lifetime sub for TiVo so in a couple years, this box will start paying for itself. Second thing I noticed was that TiVo ROCKS!!! Wow, this tuner is 10 times better than my old Cox DVR and even their normal digital tuner. Third thing I noticed was the fantastic integration of Netflix and Hulu into the box. Searching for shows not only searches cable, but also Netflix, Hulu and Amazon together so you get them all at once. It doesn't do Amazon Prime yet, but hopefully that's coming. Youtube's not too bad either, as it streams everything high def by default. Most actions are decent speed too, which is better than my Samsung TV for Inet based programming. That poor TV is dirt slow on YouTube and such. Forth thing I noticed was that TiVo's "suggestions" recording easily used up both tuners quickly in my TiVo box. So, today I'm getting this Woot and moving the 2 tuner model to the bedroom.
Yes, you will use all 4 tuners easily in a TiVo. It's just that good at finding shows that you'd want to watch with it's suggestions and the "thumbs up/down" method of rating shows that you like or dislike. Truely amazing at how good it is at this.