Stereo-Lith is an interesting option, and with newer materials it may eventually become a viable method for producing some WB prototypes such as the XXX. However, all of the stereo lith parts I've seen have been quite brittle and weak. They kind of remind one of dry angel-hair pasta, not something that I would consider very robust.
Luckily, we haven't reached the limits of conventional machining resolution. For any good machinist, +/-0.005" is a walk in the park, +/-0.001" isn't too hard to accomplish, and +/-0.0005" is still achievable. Unfortunately, with the tiny tools and such that must be used to manufacture the current waterblocks, machining costs to achieve these tolerances are very high due to the excessive time necessary to manufacture said waterblocks.
However, there are other methods for producing small, strong parts. One project I am currently working on involves the LiGA process (It's a German acronym but in English it stands for: Lithography, Electroplating, Casting). Anyone ever seen those videos of dust mites riding around on little machines? Yeah, those parts were made with the LiGA process. With this process, 5 micron (and finer) resolution is not unheard of. However, getting a single LiGA wafer made for you will cost at least $3000-$5000. A modified version of the LiGA process is a possible option for this type of prototyping, but not commonly available. What makes LiGA parts so enticing is the high strength possibilities (medium to high carbon steel type strengths). 2D is very simple to obtain with this process, true 3D parts aren't as simple,
Along the lines of the stereo lith idea would also fall SLS (Selective Laser Sintering) and metal printing. I've seen both processes, and they, too, offer great strength advantages over the plastic stereo lith parts with similar or finer resolution. However, these processes are not cheap, and metal choices may be limited.
Then we come to the question that really hurts. Is it worth it? For 99.9% of overclockers, the answer is no. The best possible waterblock we could hope to obtain by these exotic processes will allow us to run the CPU just slightly above water temperatures. Is that extra 5-10% worth the hundreds or thousands of dollars spent on building these? Only to a very few who want 'bragging rights.' There are some scientists working on this that will take heat exchangers to the absolute maximum efficiency no matter the cost, and they will be noted in history for that. I don't want to belittle the achievements of others, but it has been said many times that anyone can take exotic materials and expensive, exotic processes and create the absolute best performing product. It takes true genius to use average materials and inexpensive processes to create a product that performs 95% as well as the best but costs only 5% as much. That, my friends, is engineering in a nutshell.
It seems many are missing the forest for the trees. Many people are still caught up in the hype of waterblock design and are ignoring other issues that can yield much higher results than a new WB design. Really, look at
this thread that is over 6 months old. Many of the obvious defecencies in current watercooling were identified there, but I have seen very little if any work done on most of them. It makes me believe two things: 1.) most people are satisfied with the current level of performance in watercooled systems and/or 2.) most people are not creative/ambitious enough to go out in a different direction on their own.
Let's make an analogy to put things in perspective. If we were talking about cars, we could say that the average computer user is driving a Geo Metro (OEM aircooling) the average overclocker is driving a Monte Carlo (High end aircooling) and the average watercooler is driving a Corvette (good watercooling). There are a couple of us like Cather, JFettig, and myself who are driving Formula 1 cars or LeMans GTP cars (completely custom waterblocks, but extremely expensive). We're all interested in driving at top speed. However, to make this analogy correct, we must assume that the Corvettes and faster cars are still using farm implement tires instead of racing tires and have no suspension. It's obvious that large gains in speed could be gained by tire and suspension development, yet no one has chosen to do that because engine horsepower (WB C/W) is currently more prestigous to work on. To further slow down progress, new regulations in F1 and LeMans limit the cars to 5 gallons fuel per week (wife, kids, jobs, etc...) To make everyone go faster, it would really help if Bridgestone and BF Goodrich (new guys in WC development) started making advances in tire technology (pumps, radiators, chillers...) that provided better traction (more efficiency). Anyone wanna help out?