I have been using watercooling for over a year now and here are my tips and experiences:

It is for:
1) Those who have too much time on their hands.
2) Those who want to try new things for kicks.
3) Those who are tired of whizzing noises made by processor fans
4) Those who want a decent overclocking potential

It is not for:
1) Those who's business or important documents rely on that computer.
2) Those who are new to computing and don't know at least an intermediate level of computing hardware.
3) Those who think that WC Kits are just a matter of "Plug and Play". It's more like "Plug, sometimes play, constantly replug".

Here's the basic thing : IT TAKES TIME AND ENERGY. If you don't have those, forget it, get a powerful air cooling fan. Less maintenance and no worries about leaks.

Some tips for those who are thinking of getting one :
1) If you are a neat freak, you need to think hard. Watercooling means never having to put back the side lid of your CPU. The pipes, wire and such are gonna dangle all over the place.
2) If you are new at this, get a watercooling kit. It performs quite well compared to air cooling solutions & the parts fit nicely so you can sleep soundly for a while.
3) Basic knowledge of Physics comes in handy when maintaining these things because you can't drain all the coolant unless you tilt your computer upside down and all that funny positions to get the last drop. So knowledge of how water flows and water pressure works will save you quite some hassle and preventing spills.
4) Don't be too attracted to the UV Dyes, they look cool but aren't really friendly to your metal components. Which brings me to point 5.
5) Try to get 1 type of metal for your whole kit. Waterblock and Radiator should be either both Al or Cu. Mix them with a faulty anti-corrosive coolant and you might end up corroding the metals. But this doesn't mean single metal systems aren't excluded either by the process is slower.
6) Use generic pipes. If you use the thermaltake UV pipe, you're gonna have a tough time finding replacements from your local hardware store. But 3/8'' OD 1/4''ID works. But you need to use a blade and shave the outer part of the tube to fit.

Some tricks with Pump'n'reservoir systems.
The air bubbles are gonna get it through the motor or somehow jinx the whole thing. Although it is fine, but it is just borderline. More air goes in and you risk spoiling your whole pump. So what you can do is to drill another hole and connect it to a tube and then use a rubber stopper to stop it. When the computer is not running, open the rubber stud and let the water push the air out. But this is only applicable for pump'n'reservoir systems. Thermaltake's pumps hv included two outings to connect to a backup reservoir which serves the same purpose I describe. USE THEM. If you close and seal them like shown in the box, you're gonna have a tough time opening them a year later as the plastic is low quality and it breaks.

Distilled Water.
I haven't tried this in the long term but here's my suggestion for cheap distilled water. Battery water!. They are clean and they have to contain very little ions to make sure it doesn't spoil the car battery. Incidently it works out well for watercooling. We don't like ions, they conduct electricity, and they help with the corrosion. I also recommend that if you have Aquagate Blue coolant or the Thermaltake green coolant that you want to replace, you might want to put in battery water first to wash away the old coolant. Run it for a while to flush out all the gunk (It builds up). Then drain the distilled water as much as you can and then fill in with the brand new one.