Topic: Playback instructions
Replays are stored into your neverball directory, in which you have to copy downloaded replays in order to watch them. Under GNU/Linux and other unix-like systems, you need to copy replays in "$HOME/.neverball/".
I was sure I had mentioned this a long time ago, but maybe not? Here's my suggestion:
You can watch a replay by clicking the download link and opening the file with Neverball (e.g. neverball.exe on Windows).