I don't usually speak on this forum, though I only try when I rarely feel I may have something decent to say. I have two Yongnuo flashes, and I think they both work remarkably well for the price. I started off with a 560-II, and found it very useful, but wanted high-speed sync and auto-options, so I got a 568 EX. Both have been great choices. I use the 568 as a master and the manual 560 as a slave quite a bit, they have decent enough battery life, do the same job as any other flash I've come across, and seem decently built. At one point, I dropped the 560-II and the front plastic around the IR reciever came off. I just fixed it back into place and it still works fine. to take that as you will.
My thoughts were always "if the 568 EX, for example, does the same job as a Canon 600 RT, but costs a third the amount, then if I could buy a 568 that breaks 3 times and keep re-buying, and get the same amount of wear out of a 600 then I'd probably be doing alright. And that's exactly what Yongnuo is useful for, someone on a budget that doesn't use flash that much. Give it a try, hell, it's only like 70 bucks.