I bought a new bowtech about 3 years ago, and every thing that was made was single cam. All the new bowtechs are now dual cam. Is this just a market trend or is there new technology in this?

Well, as I understand it, bows that feature single cams inherently have less vibration and shock. The rub is that they are slower than twin cam bows. Since these new bows are full of innovative shock absorbers/dampeners, they can now keep shock and noise to lower levels while offering the higher speeds of 2 cams.

The way I understood the Bowtech lit. was that rather then have two cables that are attached to limb and cam where one cam can get out of sync with the other if its cable stretches more than the other, they are attatched to the oppocite cam locking them into sync.
Sounds like a good idea to me, but my Mathews Z-Max still kills deer, so I won't be testing Bowtechs ideas personally, this year anyway.

Bowtech's single cam line is now being sold as Diamond bows.

The new Bowtech utilize a cam system they call a Binary cam. These are twin cam bows but as Rusty pointed out the Binary system has cam to cam cables instead of the more traditional cam to limb cables.

Single cams and Binaries don't get out of sync like the old twin cam systems but they absolutely can drift out of optimum position (tune). The manuals on these bows outline the optimum position the cams should have at rest.

The Binaries store gobs of energy in the draw cycle and can be wicked fast. Because of this they can also be really tough for some folks to draw. It takes energy to store energy, no way around it.

If your Bowtech has one of the PostCam single cam systems, hang on to it! That's IMO one of the best single cam systems ever produced. You'll have to spend quite a bit of money on a new bow to beat the performance of that cam system. And even then you may be disappointed.