Water-cooling used to be only for the "extreme" tweekers / overclockers but it's becoming more mainstream as evidenced by all of the prominent heatsink manufacturers starter kits. Like Akuma said if you do it right you shouldn't have to worry about leaks. However, since it is a more "enthusiast" method of cooling your PC it's still a possibility. Most people water-cool for 2 reasons (or a combo of both):
1. Cooling. Depending on your setup you can pretty close to ambient temperature on your CPU.
2. Quiet. If that’s your goal then you can stay at or around the temps of air cooling but do it much quieter.
I've used Koolance, Swiftech, Dangerden, and Innovetek kits / parts before. I've only had 2 leaks and one was my own fault. I didn't use the fan mounting screws that came with a swiftech kit but used some of my own and accidentally punctured a fin on the radiator. This was also my first attempt at water-cooling so I didn't bother testing it out of the case before hand and it leaked all over my precious parts. I got lucky and it didn't fry anything. The other was a video card cooler by Aquagate which was bad out of the box; I did test it before I put it in my system though.
It's kind of a hobby for most folks that do it so if you're not willing to put some time into it you might want to reconsider. Do some research first. Take a look at some of these threads for ideas / suggestions:
http://forums.pcper.com/forumdisplay.php?f=35
http://www.hardforum.com/forumdisplay.php?f=91
http://forums.extremeoverclocking.com/f ... .php?f=181
http://www.ocforums.com/forumdisplay.php?f=71
My suggestion would be a swiftech kit as you get the best of both worlds in regards to quite and cooling. Something like this one:
http://www.sidewindercomputers.com/swh2licokitr1.html
If you've got some questions about setup etc let me know I'd be glad to help.
EDIT* just realized your in Canada so I'm not familiar with retailers up there at all. From the site you mentioned I would go with the Corsair kit as opposed to the Zalman kit. The Corsair for the most part is just a re-badged Swiftech anyways. Here's the link:
http://www.dangeo.com/proddetail.php?sku=51823
Here's a review of the kit:
http://www.systemcooling.com/corsair_cool-01.html