IE is well know to be breaking web standards and trying to push the web it's way. I don't use it and so can't confirm any IE issues with the forums, but if they exist then I certainly don't think that a Linux forum should change things to accomodate bad things done by IE.

Opera is a commercial browser. I don't pay for it and so I have never seen the problems with it that you seem to have. It's unlikely that the site admin pays for it either, so if problems exist he may have never seen them. If you do pay them for it, then I would suggest asking their support people why Opera doesn't render a site that Firefox does. If they provide an answer in specific information that the site is doing something that conflicts with web standards then I would advocate fixing the site. But if not then I don't think it's reasonable that the site be tested against paid commercial browsers. Of course, if you are stealing Opera than I have no concern for you. I use Firefox and don't bother to deal with warez sites to steal Opera.

I have no log-in / log-out problems. I accepted the cookie and haven't logged in in ages. If you are rejecting the cookie or playing other games with it (or have trained Opera to do strange things with the cookie), then you are likely causing yourself problems. If you are ultra paranoid about cookies, get a browser like Firefox that lets you enable or diasble cookies on a site by site basis.