I definitely get what you meant though, but, if the process of elimination doesn't help, it leaves stuff that is unfortunately much, much easier to diagnose with a quick look-see at the logs (if possible, live over SSH, at worse from a dumpMessages), than anything else, and thus can't be (accurately) reduced to a simple automated 'Yes/No'
To recap what I meant by process of elimination:
In 'cycle' mode (ie. not cover or last):
* Got the SO screensavers? Tough luck, it's an SO device, unsubscribe (See the 'Manage Your Devices' section in the 'Manage Your Kindle' page @ Amazon)
* Got the default screensavers? The install failed (which should be easy to catch during the install process itself), or the hack disabled itself for some reason (that should trigger a warning at the bottom of the screen, and in cycle mode, that's usually because the screensavers folder is empty, or was emptied by the hack because none of the stuff in it remotely looked like a valid image file (on FW 5.x, that means a png file, lowercase).
* Get the default 'Hi, I'm the screensavers hack' screen? There are no custom files in your linkss/screensavers folder
* Get the last thing shown on screen (or a blank screen on FW 2/3/4) in cycle mode, either straight-away or after a few working custom images? One of the files in your screensaver pool upset the Kindle firmware
. That rarely happens on FW 2/3/4 (you're much more likely to see a corrupted image, rather than breaking the whole thing, which is what happens on FW 5.x: once it fails in this way, only a reboot will make the framework try again, even if the next file in the cycle is okay, the framework just appears to give up on screensavers), but on FW 5.x, that means checking the size, format, resolution of each and every file in your pool, to see if it matches the device, and really is a PNG8 (optionally properly dithered down to 16 colors).
* Optionally, in shuffled cycle mode, if something specifically breaks after an autoreboot, it means I messed up
In last mode:
* It's so simple that I can't think of anything wrong ever happening ^^.
In cover mode:
* Get the default 'Hi, I'm the ScreenSavers Hack, I'm in cover mode'? Either you didn't wait long enough after opening a new book before letting the Kindle sleep, or the book format isn't supported (PDF, Topaz (+ dictionaries on FW 5.x)), or the book doesn't have a cover properly flagged in its metadata (might happen with some weird, old prc files, haven't really checked), in which case a warning is triggered on screen (in verbose mode).
* Get the cover of the next to last book you opened, not the last? Same answer as before
. (On FW 2/3/4, that might still happen for the first sleep cycle after a book switch, there's an (ugly) workaround available in the settings for that).
* Get the cover of a seemingly random book? Check that the date/time on your device is sane