2
are you using the default XOOPS cookie, or the session option? (via admin, you haveta enable session to allow people to stay logged in for a longer period of time, it seems)
i've noticed XOOPS has been kinda backwards in this regard. i recently installed xphpbb mod on a site, and it modifies the session method, so i'm testing to see if it's more accurate.
oh, and just an interesting side note, i created a Who's Online Where? block, in XOOPS System. it essentially just takes the code from the Who's Online popup that showed a user's ip and location on the site, and puts it into a block. looks good.