I have no experience with PC Watercooling but I am a Mechanical Fitter and worked for the local water corp for 5 years and now i work offshore with Oil & Gas. So I have extensive experience with tube bending/fitting, high pressure systems with pumps that have impellers the size of your living room.
Also please note I have not read anything on PC cooling nor have I read the thread fully.
This is just me putting my quick 2 cents in. If you think I might be helpful feel free to ask me some questions.
I myself can not trust the clear tubing that people use for PC Cooling! I could only imagine that it would become brittle, kink, not seal. Also probably made in china (dont get me wrong some good things come out of their of a high standard.). However we (work mates) often joke about the quality of the materials that get sold at the big hardware chains. They are oversize and undersize and can be a pest to get them to seal.
I would be inclined to go industrial with Swagelok but its hard to undo in tight spaces.With screw fittings make sure you screw the fittings on carefully because they cross thread (very fine threaded). You only need to nip them up to. No over tightening needed.
I also think that using high pressure poly for your lines would be good and the snap/push fittings work well sealing but sometimes the can be difficult to remove lines.
If you dont care about the look i would go industrial fittings from a local supplier.
Ive thought about water cooling on my rig but at the moment i dont need it. Maybe near Xmas when the 8970's have been out for a bit i might get 4 of them and if i do I will go with what i know works! I dont know if i could risk a 5k system to some cheap bits and pieces from ebay via china.