Nope: I get logged off at least twice a day (XP/IE6).
XP/IE6 too but usually only once a day and as far as I've figgered it, it's when Ted or one of his little helpers runs the daily website update. It's not a problem for me to log on again though.
I seem to be logged off whenever the daily advert in the new browser window is delivered - for example the RAC ad today (or maybe the advert is delivered as a consequence of me being logged off - who knows!).