I have been building water cooled rigs for 10 years. It's expensive and time consuming. It's also overkill for anything but the most extreme systems. And once you have more than 10 fans in your case, it's no quieter than an air-cooled rig.
As for danger with water cooling, it's there. Anybody with long-term water cooling experience, who is not a liar, can list the parts that have been ruined by leaks. In my case it's been two mobo's, and two separate graphics cards. All expensive at the time. Not to mention the hassle of replacing them. Also only one time was it an obvious leak, with water visibly splashing around (which happened in my early noobish water cooling days), and said water caused a snap, sizzle, and a pop, with a little puff of grey smoke coming from the graphics card. The other times it was the tiniest little blurble of a leak coming from a defective fitting, that I had to track down by adding UV reactive dye to the loop and find the leaky fitting with UV light. After two mobo's were killed, I finally learned not to trust anything but straight barbs with hose clamps, which is what we used to use back in the very beginning of water cooling. I've also had two pumps fail, and a water block warp a graphics card, and ruin it in about 8 months (but that was back when gfx water blocks first came out, and they are all much better now, so that probably won't happen nowadays, but you never know.) I also had a serious algae bloom happen twice (despite the use of biocides), and I had a bizarre chemical reaction happen from too much biocide which caused the water in my loop to turn into a conductive copper sulfate solution. I also experienced extreme galvanic corrosion from mixing aluminum and copper. I know you're not supposed to mix aluminum and copper, but I thought I could fight galvanic corrosion with automotive antifreeze containing pentosin, but I was wrong. So wrong. The aluminum gets removed from the aluminum parts and gets deposited on the copper parts. That's also called electro-plating. But when it happens without the application of an electric current it's just galvanic corrosion, and the electrical charge is supplied by the ions in the water. I also experienced extremely low flow from not enough pump head pressure, and cavitation from too much head pressure.
With that said, I still love the challenge and fun of building a water cooled rig. For the expense and the time however, I am growing a bit weary. Like any hobby basically, it's really for enthusiasts, and enthusiastic enthusiasts at that. It's not the most practical way to cool a computer. I don't want to discourage anybody who wants to get into water cooling, as it really is a great hobby. However, it can be even more expensive than keyboards.
In fact, right now, I am contemplating my next build as a simple, low-heat, low-noise, air-cooled rig. I am seriously considering a Haswell i7-4770s paired with a single GTX 770, in a Nanoxia DS1 case. Low heat, low noise, low hassle, and relatively low price. For data storage, I am thinking of using 2x Samsung 840 Pro 256GB SSD's (one for the OS, and one for redundant back-up, with all other storage on the cloud.) I would splurge on 32GB of RAM, probably 2133mhz or higher. For a mobo, I was thinking Gigabyte or Asrock, but nothing costing more than ~ $180. Anyway the whole rig should come in under $1,500, and it should be able to handle any game or task I throw at it. And I don't need to worry about my OC (because you can't OC the i7-4770s), and I don't need to worry about maintaining the loop or checking for leaks, or a warped gfx, or algae, or galvanic corrosion, etc. And if I want to add a second GTX770, I can just plug it in, and start gaming.
