Twin cams are mirror images of one another, and all need to be timed and creep-tuned for best performance. The Hybrids have as correctly stated above by WWAG, a power cable and control cable, along with the string, rather than two separate buss cables with outrigger yokes.
Differences-
Twins have straight nock travel, but not level because the true centerline of the bow is the gripm and the rest rides above that--with "mirror" cams, the nock point ends up starting out high, not level. Hybrids offer both straight and level due to the round cable track and the control cable which "monitors" precise synch. This constitutes better efficiency and wider range of acceptable arrow spine, resulting in more forgiveness and accuracy.
Hybrids generally tend to be quieter than twins.
Some Hybrids come with directions and timing marks that are easy to read, and everything is laid out for the dealer or customer to set the bow for best performance and S&LNT---set them, forget them, go shoot, enjoy.
Twins shoot very well, and have for many years. But there is a new design in town now that works easier and better IMHO, one that offers the best of both twin and solocam worlds, and S&LNT to boot. My scores have increased considerably since I've switched to the Merlin Omega hybrid from their twin cams, with higher 12,11,and X counts. Our Factory Pro staff for 2004 are seeing similar results after having also mostly shot twins for a number of years.
Up to each person to decide what will prove to be the best system for their intended application, but there are some points to chew on.
Good shooting, Pinwheel 12