Cannon+Cannon are very accurate, at least as long as your AI turrets are not trying to hit a very small very fast target. Beam+Cannon are good, but again have a little more trouble than c+c at hitting small fast targets. Cannon+Missile last I checked didn't work with AI, but that was in the prebuild haven't tryed it in 0.201.126. Beam+Missile I have not gotten around to testing. Cannon+Beam turrets have storm-trooper accuracy if you do not fix it in the blockbehavior.config. Beam+Beam now works with AI, but like c+b has to be tweaked in the blockbehavior.config if you want to hit anything when it is mounted on a turret. As for Misses well Missile+Cannon seams to work but I have not tested it enough, the AI is too dumb to use Missile+Missile, and I had no real problems with Missile+Beam.
Whups I forgot the normal weapons
I don't know what to say about them I almost never use Cannon on its own so not sure how its accuracy is when used by AI, same for Missiles, Beams I have tested and they seam to hit often enough, not sure how I fell about the lock on thing, I guess it will make Star Trek fans happy but other than that I think it looks a little odd.
As for using the weapons my self I have no real issues Cannons for me are easy to use, Beams are all so relatively easy to use though if your camera is in the wrong place you can blind yourself, and missiles seam to be working again unlike in the prebuild. I also fined the new UI to be a good improvement, but there is always room for more improvement.
Over all I think it is a great update, but of course with any new system there are a few teething issues that will have to be dealt with. I also find performance has improved quite a bit.