Mike Wong from plug-in developer onOne has posted some details about their Photoshop compatibility roadmap. He writes:
Windows versions of our plug-ins have been 64-bit now for months… We are converting our plug-ins over to be 64-bit compatible on the Mac OS X side… Our goal is to have Photoshop CS5 compatible updates for the current versions of our plug-ins available within 30 days of Photoshop CS5 being made widely available…. That means we should have everything out there for you to download by June 12, 2010.
More generally, 32-bit Mac plug-ins should run just fine in Photoshop CS5, provided you choose the “Open in 32-bit mode” option in Get Info. That’s analogous to the situation on Windows, where you can run your older plug-ins in the 32-bit version of the app. (On Mac Photoshop is a single 32/64-bit binary, whereas on Windows it’s two discreet apps.)
I’ll post news about other developers’ 64-bit migration plans as I get it, and I look forward to sharing some great Mac 64-bit benchmarks soon.