We've been using your solution for some monthes now, and had no problem with it, no matter what version or server.
On one server, the Web Services are quite strange and throw me away two times ( 401 Unauthorized ).
The good thing is that your solution or Ajax seems to call it again each time, so the user doesn't notice it.
The problem came just this morning, when the person in charge of the server changed Sharepoint site collection into HTTPS.
I couldn't log on, so I don't have any more clue than the fact that the services didn't send me the data, so my graphs drew empty squares.
There are not that much things I can think of for that, and one of these is SPServices.
Well, in fact, I already used the exact same script on an HTTPS site, and all went good, but I just can't figure how it could be possible that Web Services do not send me data on a specific case.
I wanted to ask if there is any way to be sure that the problem came from SPServices, so I can tell the guy that he has to fix the Web Services when he put HTTPS back.
On a related note, I never specify an URL, not even by calling methods that coudl give me it, so it should put HTTPS instead of HTTP automatically I guess.
Sorry for the question that probably won't really help anyone, but I prefer to be sure that I didn't miss something while investigating what I can.