I made a gem called em-resque [1] for running Resque workers inside an EventMachine. It was fast, but the lack of good libraries, like Curl::Easy for evented code was a big problem. Also the exceptions EventMachine gave us or the lack of exceptions when missing work items was just plain awful. We spent several months catching these bugs and made even some progress together with nice folks from resque-retry and Resque teams.
Then I had a chance to re-build the system. I couldn't be more happy with it. It scales well, it's pretty fault proof and almost as fast as my EventMachine solution. Threads are slow, but the real slowness comes from the IO. Now instead of em-http-request I have much better working Curl::Easy and the whole codebase is much easier to understand.
EDIT: It seemed familiar, so I dug up an old thread of yours [1], where we discussed a similar thing. At that time, it seemed you narrowed down your problems to Eventmachine, but were still using Redis. Has that changed ?
[1] http://news.ycombinator.com/item?id=3366470