It's definitely a caffeine thing, but it's the sugar too. Coffee doesn't do it for me.
So, I'm trying Hansen's black cherry as a way to wean myself off slowly, but that's caffeine free, so...
SodaStream isn't better for the environment than bottles and cans? That's disappointing.
The reason they're not better for the environment is because of all of the little pod things that you use with the machine, similar to the Keurig coffee makers and so on. I don't believe you can recycle those normally. The company does have a program where they send you a mailer and you can then the things to them, but I rather doubt most people take advantage of that (laziness) and simply throw them away. I read a thing about it and will edit this post in a bit with a link.
[edit]
The thing I was thinking about are primarily the coffee pods, but I did some looking into SodaStream specifically and found these two pieces.
For the environmentally conscious, the junk that ends up in landfills is not, and cannot be, the only consideration; there is also the carbon footprint of manufacture and transportation, as well as materials used, for each method of soft drink consumption. Whether you buy bottles and cans and then recycle those, or use a SodaStream, you will still have those costs. The potential savings, for both money and the environment, comes in whether you can drink enough carbonated beverages made with the SodaStream to make the switch worthwhile, and this of course depends on the individual user.
As for the caffeine, you might also try using other sources, and you can get it in pill form. I think you just have to weigh the benefits of cutting out soda (considerable), even diet soda, with all of the other stuff that comes with drinking soda. You're used to the caffeine, you're used to the carbonation, you're used to the sweetness, you're used to the flavors. I think if you can find replacements for most of those, the switch might not be so bad.