Well, ibill was definitely down completely for at least 45 minutes this morning while I was one.. CMI page, signup page, etc. Appeared their network was down.
They appear to be back up though.. Hopefully they were not down too long.
As for previous problems, I can't speak to those. I just started using a sponsor that uses ibill, and this was the first day I was sending any sort of real traffic to them.
-Phil