Like the rest of you, I just downgraded my Calendar by "upgrading" to Mountain Lion.
In my opinion, the problem is that they are trying to make things like the Calendar and Mail uniform across all devices (i.e. iPad, iPhone, MacBook) Although it is extremely helpful for these applications to share the data via iCloud, dumbing down my MacBook does not seem like a logical way to go. I have an iPhone and my MacBook. I do not own an iPad at this time because I "foolishly" want the full functionality of a computer. It doesn't bother me as much that my iPhone doesn't allow me to customize the snooze setting for alarms and alerts because I expect it to have more limitations based on its operating system, smaller size, and smaller memory. However, I have absolutely no understanding why Apple would take away functionality that the MacBook has already proven itself to be capable of so that it can more fully emulate its lesser counterparts.
I appreciate the creative solutions that some of you have offered up as workarounds, but it is appalling if Apple thinks it is acceptable for users to have to go through so many combersome steps after "upgrading" do accomplish something that was so elegantly and efficiently achieved in the "downgraded" version.
please, Please, PLEASE put the customizable snooze back in just the way it was. It wasn't broken before, but it sure is now! I can't help but believe this has to be a bug, so I just got through reporting it as such.