I recently purchased a knitting machine from my mother-in-law. It works pretty well, but it is not entirely stress-free or anything. I had to order a new sponge bar for it. It looks pretty cool sitting in my upstairs guest room--even though it takes up a lot of space. I knitted a vest on it that is waiting to be sewn together. It is made from Andean Treasure from KnitPicks. I wouldn't recommend using this yarn on a knitting machine. There were quite a few knots in the balls of yarn and these are murder on a knitting machine--but I managed because it is what I had on hand. I think it is going to make a great sweater!
Here is a sample that I knit on the machine out of Nature Spun Sport. I bought the yarn on eBay...a GREAT source for cone yarn. I don't think I'll use the pattern for my next project because it kinda tore up the edges of the swatch.