I tried to dig deeper to em-activerecord, but it really was a better idea to build a very simple orm layer with specific sql queries instead of a more complex solution.
This problem is noted by the developers of em-activerecord and em-synchrony a several months ago already. There seems to be no progress, which might lead to a harder problem or that people are not using these libraries in bigger services.
But my point was, that Node.js seems to be much much more finished product compared to EventMachine for example. With EM you have to live without most of the Rails and for example testing the EM code with unit tests is not so nice job to do...
What I liked the most with EM are the Ruby fibers. The best solution for hiding the callbacks and writing nice and readable code by far. Too bad the fibers are a bit of a ghetto still, like somebody said earlier.
This seems like exactly what would hit anybody who is trying to build a worker model for processing data... hell even for sending emails. It would be interesting to see where you are pushing the limits - it could even be something deep like