9
If you want proper integration then you have to use koudanshi's conversion scripts. Then you will have all users and links as part of the XOOPS site. Be aware though the XOOPS IPB module (from Koudanshi) makes changes to core files, so you have to wait for HIS updates when XOOPS core changes. That said, its a good module.
On my site the iframe simply provides a scroll bar when the page exceeds the frame length, however, I have made forum posts/ per page quite small, so this may not occur.
The version I have is not limited, not timed. It's fully functional but not supported. (at least not by IPB official) There are however other third party sites that DO support IPB software ie IBPlanet, but I've not seen that around for a bit. Its very popular however and there are loads of usergroups around.
As I said, iframes are not a perferct solution, but I do want to preserve my XOOPS core files AND have the benefits of a flexible forum. It's a matter of personal choice, I think.
When The XOOPS forum gives me the moderation and other features that I want, then I will change my options.