On Nik software's website it's very confusing as to whether or not the recently released version 3 of Silver Efex Pro (one of my favorite plug ins) runs in 64bit in Aperture 3. On the products information page, under the compatibility tab it states that it runs in 32bit on Aperture 3 but offers a link to more information about 64 bit compatibility. Going to this page it states that:
"Viveza 2, HDR Efex Pro, Color Efex Pro 3.0, and Silver Efex Pro are all now 64-bit compatible. To download the free 64-bit update"
however immediately below that there is a section on Aperture compatibility where it says that:
"All Nik Software plug-ins (Dfine 2.0, Viveza 2, Color Efex Pro 3.0, Silver Efex Pro, and Sharpener Pro 3.0) are fully compatible with Aperture 3 while in 32-bit mode. For more information about future 64-bit support click here."
The click here bringing you to the same page. Like I said, confusing. Anyway, I downloaded the trial version and it is indeed 64bit. So if you were wondering you now have a definitive answer.