Is this useful?

Just came across it, feedback would be nice!

Neat, but screw buying it. Looks like you could build one if you have some ingenuity. Personally, I don't mind hooking up my co2 tank to my PET bottles every now and then when I want to carb or re-carb something.

Very neat and a good idea. It's probably pretty inexpensive or will be at some point and if I didn't have a co2 tank and carbonator cap (you know, like the other millions of people in the us who don't make their own beer or sodas), then I would get one. Before I got into this, I definately would have gotten one, since I drink slowly and would keep it upside down in the fridge like that. (I'd probably guess the price at 10-20 bucks, and with enough of a production run, 9.99 meaning that it would be accessable to everyone who normally drinks soda but doesn't get all the equipment we do.)
I do expect the soda to be somewhat flatter towards the end, but not totally flat. It's a natural progression of equilibrium, and happens when I dispense soda or beer from my kegs and don't have the co2 going, but with 2 liters (or less, since this would work with smaller bottles that have the same thread diameter) I don't think it would be noticiable.

You know what... In the other thread, how we were talking about a seltzer recarb and losing co2 (in which I take to mean the constant opening and closing and venting of co2), I'd still probably get one, but I'd probably spray paint most of it and make a cover for it. Or as alchemedes said, try to make one or two. And use them when going places with precarbed water. That said... I could probably do the same thing with a bottle with a carbonator cap, a ball lock, hose and a picnic tap. Think I'll go sketch some ideas tonight. It's mostly for design, since I'm sure that even if I prop it up on a plain cardboard box as is, it'd cost slightly more to make than buy. With design, I'm probably just coming up with a simple stand (cardboard probably) and a cover of what I might want it to look like. Glue some gears on, that sort of thing.

Yeah man, please enforce your design and see how it works, I will definitely be interested in doing something like that too!

Can the ball lock act as dispenser too? I thought it only took out to the bottle and not the other way around? But I don't know I'm new to all this, hehe.

Yup, if you have kegs, then you'll have the two types of locks (gas and liquid). They're pretty close to the same, but I think there's one difference but I don't recall what to the locks. But you could use a gas pin/ball lock to act as a dispenser. You generally do need to connect this to the "in" post due to the difference (size? lock height?). If you have the bottle (or keg) with the pins at the bottom, then you would use the "in" post as the dispenser and the "out" post as the gas fill. There's a method of not using gas to push the beer out of a keg that does this, and depending on the place, will use gas to keep the beer at a stable carb, rather than getting flatter towards the end. (Some also say that it invalidates the method). That's why I would consider
1) an upside down soda bottle with gas lock, carbonator cap, really short hose and tap. (They also have taps that are just the ball lock and metal tap, but I'm cheap for this).
2) wire coat hangers to act as a frame, that could allow frozen gel packs to surround the bottle to keep it cold
3) a nice looking base that will also collect the condensation from the gel packs and also contain weights to keep the full bottle from tipping
4) a cover with some sort of design on it.

I could probably use some scrap wood for the frame too, but it makes it bulkier. The main thing would wind up being, how do I want the outside to look. (Make it a clock, make it look like a soda/beer can, make it obscene, make it copper with gears and pipes and smoke stacks, make it look like a building) that sort of thing.