Wow, it has been a full year since I originally started this thread. Support has again seemed to drop off; however, FWIW, Gavin has provided a work-around for Snow Leopard users. According to another customer, version 1.0.6 has been working. I can confirm that on my system (Macbook Pro 2.66 GHz, 10.6.3) I have been running this version and it appears stable.
This is not a solution, but a workaround that is at least keeping me up and running. I would like to see an official release that supports my processor and version of OS X. Until then, I suggest running 1.0.6:
http://futureaudioworkshop.com/downloads/download.php?file=Circle-1.0.6-setup.dmg
Gavin, please let your customers know that you're still working on a supported update. You had started a good trend of keeping us in the loop, and now that seems to have dropped off. I hope you continue to develop your awesome software.