I have been getting that same message for some time now. The only thing I've noticed is that it will not give me the option of selecting my user name (through the drop down thing) any longer.
What they're saying actually is true; if the usernames and passwords are not submitted via encrypted connection, they will appear as clear text in the data packets. Someone would have to actively "sniff" for them, but that's hacker 101 stuff. So basically your CC info is safe, but passwords could be "easily" stolen. Has the forum software posted any updates for this issue? It's really on them to fix it. And it really is a problem.
Is all this techno stuff why, all of a sudden, I have to sign in every time I get on the site, even though I check "Keep Me Logged In"?
I was having issues with signing in every time too...then all of a sudden my bookmark went away...had to re-mark it, now its seems fine today...guess this explains it...