I think the longest I will wait and have waited on hold is about an hour. Any more than that, and I am usually gone, but depends on my mood.
If I am totally frustrated with the company, then I will hold as long as needed so I can get somewhere with them. Otherwise, basic stuff, max a few minutes and I will try back later. My biggest peeve is the same music over and over with no status messages.
I prefer to have the on hold things like "You are number 49 out of 1404 in line to be served" type of thing.