Put the Gates Carbon Timing belt on our 2008 Robusta today.
The installation was pretty easy. The only significant problem was clearence between the stoker's timing ring, and the chainstay. (The chainrings used for this system are wider than a conventional chainring.) Web Cyclery has a good piece on their website, on retrofitting the Gates system on Co-Motion Tandems http://webcyclery.com/pages.php?pageid=72. They recommend a 2mm chainring bolt spacer.
Being an impatient sort, not wanting to wait to get chainring spacers delivered on line, I bought 3/8 inch washers at the hardware store, dremeled down one side to make them fit, and they worked fine (and saved $10 in the process).
According to Gates, chain line is critical to this setup. I was able to fine tune the chainline by sliding the eccentric sideways, and with a few mintues playing around pretty much had it dialed in.
We road it afterwards for about an hour, and tested it out, with some hard efforts standiing out of the saddle, and some high rpm sprints, with no problems.
It definitely is lighter. Claimed weight reduction is 10 ounces. I didn't put the parts on a scale, but it is clear that is lighter. The Gates' rings are slightly heavier than conventional chaing rings. However the belt is dramatically lighter than a timing chain.
This is getting long, so I'll save riding impressions for another post.