If you are currently running any BOINC CUDA projects (not just PrimeGrid) on an Nvidia GPU we recommend that you do NOT UPGRADE to OS X 10.9 (Mavericks) at this time. According to the BOINC Wiki, the Nvidia CUDA driver is broken. After ugrading to OS X 10.9, you will likely be unable to run any BOINC CUDA tasks until Nvidia fixes the driver. There's an ongoing discussion located here.
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