I'm using a TiVo with Dish Network. (I also have a 501 and two Direct TV TiVo receivers, so I'll take a crack at your questions.)
Setup is easy, but long. TiVo sits between your receiver and your television, buffering the broadcast. What takes time is, after the initial phone call to get your listings, TiVo has to sort and process the listings data. Because of the large number of channels available in the Dish Network lineup, it takes a few hours. You might want to set it up before bedtime (figure on half an hour or so), and let it do its thing overnight. The subsequent daily calls are transparent and don't interfere with your viewing and recording.
TiVo does lose a little quality because it recompresses the signal again and decompresses it for viewing. As you probably know, TiVo has 4 quality settings: Best, High, Medium, and Basic. I usually use Medium and I'm satisfied. For some sporting events with fast action, High works better. I'll caution you that I'm using a 27" TV. Folks with larger televisions see more quality deterioration.
I usually prefer the TiVo to the 501. The reason is the way TiVo schedules its recordings. With the 501, when you set a recurring recording, it simply records the same channel and time period that you tell it to. If the network changes its programming, the 501 merrily records whatever is broadcast.
With TiVo, when you set a Season Pass, it finds the program on the channel you specify and records it, whenever it's on. I like "Ed" on NBC, and in its first season, it moved from Sunday night to Wednesday night in midseason. I didn't even know it had moved. If I had set the recording on the 501, it would have continued to record the Sunday timeslot and I would have had to search for where it had moved.
With a TiVo Season Pass, you also have the option of recording only first-run episodes and ignoring reruns. TiVo will also not record the same episode within 28 days, unless you ask it to. TiVo is also smart enough to reschedule an episode if it can if it misses the first one. Just yesterday, I had lost the signal during a storm when I had asked TiVo to record a program. There was a later showing that TiVo went and got for me.
TiVo's conflict management is also better. You can rank your season passes so that, when programs move around and two of your requested recordings are aired at the same time, it will choose the one with the higher priority. The 501 will tell you have a conflict and ask you what to record. If two recurring recordings conflict, you have to cancel one of them (and set it up again later if its a one-time conflict).
TiVo will also use its unused space for Suggestions. When you are not using the receiver to record or are watching recorded programming, TiVo will fill its empty space with other programs it thinks you may like based on what you record. Some people find it intrusive; I appreciate it. And you can turn off the feature if you wish. (With the feature turned off, TiVo still generates a suggestions list you can review and select from.) With as many channels as Dish Network offers, I find TiVo's suggestions are helpful in finding things I like to watch. It has found some programs I have really enjoyed that I didn't even know existed. Of course, it's found some dogs, too, but they are easily ignored or deleted.
The price of a 60-hour (at basic quality, around 35 at medium) is $399, plus $12.95 a month or $249 lifetime of the receiver for the service). I'm not sure of the Dish Network deals for new subscribers, so I'll leave that for someone more knowledgeable.
My order of preference for my receivers is 1) the DirecTV TiVos (for the satellite quality and TiVo features); 2) TiVo with Dish Network (for Tivo features); and 3) the 501 (for satellite quality).
Of course, your mileage may vary, but that's my opinion, and I'm stickiin' to it.
