Tivo and Series 3
Those two questions are a mine field. I'll do my best.
Tansferring shows between tivo and mac. This can be done through Roxio Toast v10 (as well as tivo to mac.) There's also freeware to do this, but I haven't had the best results with it. More specifically, it was slow.
Transferring from Tivo to mac has an important caveat: most HD content is generally marked by your service provider to prevent HD transfer. Some cable operators are marking SD video, too. You have to check the situation with your provider. It can do your head in. I cannot transfer Show X from Tivo to Mac. Yet, I can watch it on demand to record to my Mac. Brilliant.
There's no restriction on mac -> tivo. Visual Hub also had a mac to tivo option that worked really well, too but that's no longer an option as the company is done.
Roxio also makes software for the PC for this trick. Same restrictions apply. I'm not a pc expert, so I'll leave it for someone else to fill in the blanks.
Getting the video to portable devices? Roxio will convert pretty much any format to ipod or ipad with the exception of MKV. This includes files pulled from your tivo. That's if you load files. The downside is time. Nothing is more frustrating than waiting to leave to go somewhere, and then counting the minutes as you wait for a tivo transfer, conversion or ipod load. I've had some hectic airport moments due to this.
Series 2 Tivos can transfer any content back/forth but they're not HD. Once you go hd, it's hard to go back.
El gato does allow the option to stream through the internet to your devices. It will require a $5 or so app. My personal experience (which i do not claim to be representative of everyone) is it's buggy at best. I generally find things work great for a few minutes, then it all goes pear-shaped.
I've had a much better experience with a Slingplayer Solo. I use this with my ipad, and I can watch virtually anything anywhere with no problem. I tend to prefer this over hotel tv. The downside is cost. You've just added another $200 for hardware and slingplayer app. That assumes you have wired internet near the sling, no one else changing the channels on that set, and time to mess around with the configuration. The config isn't that bad if you have a simple one. I have an airport to airport which took about two days to get just right. On the positive note: I can watch anything remotely (tivos or cable) that I would just like being at home.) Well, almost like home. The quality is generally good, but it helps to be a distance away from the ipod, ipad or laptop depending on what you're using.
A couple of things to keep in mind: Netflix now has an app for the ipad, iphone and mac. It's a cheap pay as you go option if you don't want to invest in hardware. Doesn't help you at all if you're a sports fan, and need to see games outside of your home market.
HBO has stated their building an iPad app to stream content for subscribers for free. That could be really sweet.
Verizon has stated they're considering offering a sling like functionality with FIIOS. Not sure if I believe them (or if it'll be for free.)
I'll note I didn't start my "project" of remote media viewing to become an expert. It was a case of fiddling until I made it to the most optimal set-up. In my case it's a Series 3 tivo (2 of them) to a slingplayer to an airport to another airport to the world. That's a lot of expense for hardware. You got to think how bad do I want it, and what else you can use the money!
Hope that helps. Let me know if you need more information.