I've had a Sodastream home carbonator thingy for a couple of years now. I love it. I really enjoy carbonated beverages, and the Sodastream is an easy way to inexpensively have a lot of variety of pop (or, soda, if you're from the West) at hand.
I have to admit that I approached the whole idea with some trepidation. But my fears were unwarranted as the Sodastream is easy, clean, and fast to use. Dare I say it is even a little fun? Even if you don't enjoy it, you will enjoy learning just how little materials are used in making soda and how much price-gouging the big guys engage in.
The Sodastream model that I have is pictured below. I don't know exactly which one this is because they make a dizzying array of seemingly barely distinguishable models. (Seriously, wtf?) Presumably they all work the same, and aside from some unnecessary accessories, the models are interchangeable. If I were buying one today, I'd probably get this one.
Now on with the tips!
For the first year or so, Sur La Table was the best place to buy refilled gas canisters. But Sodastream seems to have really expanded their distribution so there are a lot more places now. Nonetheless, Sur La Table will often let you sample flavors so it's worth stopping by a location near you.
Now that you can find Sodastream consumables in lots of stores, you might not need to ever visit the Sodastream website, but it's still a great place to buy syrup. The selection is better, and if you sign up for their email newsletter, they often have coupons to save on shipping.
Although the Sodastream instructions say to carbonate your bottles until you hear three "buzzes," I found that two buzzes is sufficient. You might like more, or less, carbonation. Experiment, and if two works for you, your gas canisters will last longer.
Similarly,experiment with how much syrup you use. The fill-lines inside the cap are just suggestions (if you can even see them, I find them rather inscrutable) and keep in mind the "best" amount of syrup will vary by flavor. For example, I prefer less Ginger Ale syrup than I do Root Beer.
My friend Nate understands physics better than I do, and he suggests that chilling the water before carbonating it will use less gas. Subjectively, I agree.
Also courtesy of Nate, be sure to heed the warning that you must add the syrup after carbonating the water. If you do it before, you'll regret it. Although I understand the resulting geyser is spectacular.
If you enjoy a cocktail on occasion, you need a Sodastream. Period. Keep a bottle of just soda water and your home libations will never be the same. Trust me.
Buy an extra canister of gas if you can afford it. It's a lot more convenient to have a spare on hand.
I might periodically update this list as I discover or learn of more. (Please let me know of your own!)