@edwecarlo - yeah I am still awaiting the technical details from them, I haven't looked at the code to try to guess in advance of it. That they said a few users had their IP blocked implies that those specific users were flooding the api, which means there is some feature in the plugin that escapes my 50 books at a time limit. I could make random guesses or speculate from looking at the code but I really want to hear from their tech team as to what triggered it from their side.
And you are absolutely correct that all users share the same developer key for this plugin, so simultaneous usage by thousands of users would in theory be an issue. It really depends on how they do their throttling. I originally thought they would disable the developer key if the threshold gets hit. It seems that is their action of last resort which hopefully we can workaround to avoid. Instead they blocked some IPs. Was this because a couple of people were randomly chosen as "victims" due to a whole bunch of other users also simultaneously using the plugin? Or does their blocking have more intelligence and target only specific IPs which are exceeding their limits? Only their tech team can tell me that, hopefully it is the latter.
I did have a conversation with one of their team a long time ago when writing this plugin to try to figure out if it would become an issue if the plugin got very popular. At the time I was told that the measuring is done as an average over a time period.
Another suggestion from a user ages ago was using multiple developer keys, even getting users to register to use an individual key. However as I said back then I believe that is completely and totally against the spirit and intent of the API and their T&Cs. And if Goodreads are blocking specific IPs that are flooding their API then using a different key wouldn't achieve much anyway.
So... we wait for their response. The original support person did not have the technical details I need so handed it off to their tech team.
As I said above if anyone reading this happened to be someone who had their Goodreads account blocked and can hence provide any hints as to what may have happened to them please do get in touch with me via any means. This isn't a witch hunt, I am not grumpy about it or anything like that. It could be that some feature just has to be changed or that I petition Goodreads for an api change to reduce the calls I need to make.