You GOT it!
Like the quote button, you CAN just highlight what you want to hide (like you would highlight what you want to quote) and then hit the spoiler button. And you can leave the box that shows in the popup blank and it still works.But I had to MANUALLY fix what the SPOILER button in the ribbon did - the first entry was what was the result of using the spoiler button - it isn't working.
Let me try to say it more clearly: I clicked on the SPOILER button. It presented me with a box to type in. I typed This is what I'm HIDING and then clicked Continue.
The following (minus the spaces) showed up in my typing box: [ SPOILER="This is what I'm HIDING"][/SPOILER ] - clearly, that's wrong - there should be no =, no quotes, and the close bracket should be BEFORE the text that is the spoiler text.
I'm hoping that is one of the things I get fixed.smilie withdrawal...