Is Photoshop elements 10 compatible with Mountain Lion?
PSE 6, 8, 9, 10, and 11 are compatible with 10.8.
The link should answer your query in more detailed way - http://forums.adobe.com/message/4527508#4527508
Except that it's not correct, only official. The other versions I listed work. They just aren't officially supported, but since there's no support for anything but the current version in any operating system anyway, it's totally irrelevant.