I've brewed it probably 4 or 5 times. It takes awhile to get the first culture started (2 smaller throw away batches, in my experience). I've bought a culture once, but I realized you can just buy a plain GT's kombucha in the store and start a culture from the unstrained floaties at the bottom.
I am slightly concerned about harmful bacteria somehow culturing onto the scoby ("symbiotic colony of bacteria and yeasts"), however this is SUPPOSED to be obvious and discoloration should be an indicator. I probably wouldn't brew it if I were in a older house or humid environment, but that's just me.
The hard part is keeping the fizz and finding the right flavorings. The last couple times I tried, I was working on perfecting a chai/vanilla flavoring. I also tried to bottle the stuff in hopes of keeping the carbonation. I kinda got bored and lazy with it and gave up. Though it is pretty good stuff and DEFINITELY not worth paying $4 a bottle.
The probiotic effect seems minor, but there may be stronger cultures to start from. In my brew days, I used to drink 16-20 oz a day with no problem, but it is very sugary and I wouldn't recommend drinking it daily. If I ever start brewing again, I'll post.
Anyone else home brew this stuff with any success?