I just snagged an SX500IS with 1.00c FW...
STICK now recognizes it and downloads the appropriate firmware.
It booted up CHDK ok, although there seems to be a lot of fighting going on between the camera display and CHDK. There are also some menu options missing that I think
should be there, but aren't. I'm not completely sure of that, as I haven't spent much time with it yet. I'll see if I can burn some time this weekend and run through everything to see what does and doesn't work.
Regardless, thanks for work on this... I'll be happy to troubleshoot whatever I can, but you may have to exercise some patience with me.