I have done it on and off for a few years. I have only done it will my more established plants though. I typically water like normal with coffee every 2 to 3 months and there are some noticeable increases in growth. I wish I had taken pictures but after a small stoppage in application I put a little extra on my lowii x boschiana and the leaves went from about 4 inches long to about 14 in span of 5 months(guestimating). The pitchers for me however seemed to be less colorful and smaller overall after it has one of these growth spurts, however, if I don't water with coffee it produces its normal pitchers again. The moss also goes crazy for me as well which is nice since I don't have to much of it to start with. I usually just take left over grounds and throw them in some water and let it sit for a day. Before use I will shake it up and water as normal. I have never been very diligent with flushing the pots though but have noticed no real issues (I would still recommend it if possible).
It'll be interesting to see what it looks like in a few months though! Keep us updated. I also know there are a few threads out and about if you have any other questions.