I have a Hackinosh that I built a couple of years ago. It is a Gigabyte GA-Z68MA-D2H-B3, I5 2500k, Nvidia GT640 2GB. I have upgraded from Snow Leopard to Lion to Mavericks with no major problems. Until this week, I was running 10.9.2. I didn’t want to upgrade to 10.9.3 until I had free time in case I ran into any problems.
10.9.4 came out a couple of weeks ago and I had vacation this week so I decided to run the combo update. My fears were unfounded. My machine updated to 10.9.4 with no issues whatsoever, I ran Multibeast and reinstalled audio, and I have had no problems.
It took me about 30 minutes from start (download the Combo Update) to finish (boot into OSX 10.9.4 with working audio).
I am very satisfied and impressed. My webcam was not working with 10.9.2, but it works perfectly with 10.9.4.