The plugin is very useful, specially when writing movie reviews.
The only problem is that the look of the tags hiding the text (the "Spoiler" image) is not very refine. I suggest other options like blurring or fading the hidden text.
Another good solution would be to replace all the spoiler text, without leaving blank spaces or lines, by a "Spoiler" button. Hovering whith the mouse on the button we could see a message (customazible if possible) like: "Click here if you want to read the text with spoilers". And the clicking display the text.