I keep planning to use mineral oil but I still have not. Maybe in the future. I use just off the shelf stuff and then i end up handing it over. It is just the power consumption of the newer things is starting to make sense especially with xeon CPUs and other lower powered things if you leave your stuff on 24/7.
I considered water cooling for my GTX-970 but since it's a reference design, the VRMs really aren't capable of supplying enough current to OC the gpu to any meaningful extent. The Stock fan cooler is plenty capable (albeit with a custom fan speed profile) of cooling everything. The only advantage I see with water cooling in most circumstances nowadays is that, you may get longer component life by keeping them running at cooler temps and if you use a see-thru side window, you can have a slick looking rig. Otherwise, it's a lot of expense. I guess it depends on what the limiting factor is. For my reference design PNY GTX-970, I ran into a ceiling in on-card power delivery components which I don't think would benefit from water cooling. Also the factory BIOS would not allow for more than 107% power and hacked BIOS were not available and seemingly not going to be.