First of all, DNN is not supposed to store any passwords, so the password they are having them e-mailed back to them "should" be the one used when the account was first created in DNN.  But, then again, I don't remember the exact details of how that was working in the 4.7 version.  In any case, don't rely upon the password that is e-mailed to a user, it is not used in the authentication module.

Second, if it is the same users over and over again, check their computers to see if there is anything out of the ordinary installed on those computers that might be causing problems like that.  Spyware and Malware programs are notorious for doing things like that.  

Third, it might benefit you to figure out whether it is a DNN problem or a workstation problem, so you can narrow down your direction in trouble-shooting.  The simplest way is to have those users log into a computer that you "know" is working good and see if they get logged out there also.   That will tell you whether you should be looking at DNN or the computer for answers.

Thanks so much for everyone's suggestions.  The problem is that it is seemingly totally random.  They will be logged in fine for weeks, then suddenly they will get logged out.  Giving them another PC is not really an option in this case.  And we are pretty tightly controlled with corporate virus/spyware, but that is a good suggestion, I will double-check these machines to make sure there's nothing infecting them.

I didn't know that about the passwords.  How do check to see what version of AD authentication I'm using?  I don't see a version in my web.config, and my site just says:

Thanks again for everyone's help, I really appreciate it!