The "Photoshop failed to initialize due to a program error" message I reported earlier and have heard from others about can be traced to a single item: Nik's HDR Efex Pro. Uninstall it and Photoshop works as expected. The hint was watching what was being fetched in the dialog box updates as Photoshop loads. I've sent messages into Adobe's customer support staff to alert them to the issue.
Nik seems to be aware of a problem and has posted a troubleshooting page for HDR Efex Pro. However, it doesn't work for me because...oops, "Too Many Activations." FWIW, Nik Customer Support did not get back to me as they promised (now five days and running). It's incidents like this that make me reconsider my recommendations (right now Nik's Complete Suite is one of my recommended software products).