Not granite here, I have soapstone so I can't answer your question regarding fabrication. But I love my runnels. And yes it drains into the sink. There is a slope to them. Here's a pic.

There are a number of really good threads on this topic. I found a bunch that I hadn't seen before using:

http://www.google.com/search?q=site:gardenweb.com+runnels+drain

Below, I link one of the better threads.

Here is a link that might be useful: runnels thread

My runnels were done terribly and I still love them. Well, love is a strong word, but I am happy to have crappy runnels!

I have a vintage sink with an integrated drainboard on the side and I love not keeping a dish drainer basket any more. The built in runnels help dry dishes and encourage you to put things away sooner.

I agree with dianalo, I do put things away sooner. My new runnels got quite the workout today as I canned tuna. From drying the jars to using the runnels as a run-off area for my tuna cutting board. Any small bits of tuna just wiped down into the sink, without problems.

I don't know what I did before my runnels.... oh, yeah, I had that ugly drying rack on the counter!

I was going to do runnels but decided to do an drainboard instead after seeing elizpiz's kitchen.