My husband had a serious habit - he drank in the morning, throughout the day and the evening - he was and remains a seltzer fanatic. Then we brought the Sodastream into his life and now he's a changed man - he can make his own seltzer for a fraction of the cost and without tearing through seemingly millions of plastic bottles to get his fix. I highly, highly recommend it!
Also, for those of you wondering, the CO2 cartridges are exchanged at any store carrying the products - for $14.99 you get a recycled cylinder and yours is sent back to the company. That's $14.99 for ~65 bottles of whatever carbonated treat tickles your fancy. Again, highly recommended.