Just to chime in with my experience here, I tend to agree it is location/speed based. I'm in Australia in a remote location, so very slow ADSL.
It does not matter what browser, PC, home or company internet, time of day, etc but I always have "Session Timeout" issues navigating the site, sometimes can't get logged in for ages, etc.
I've just put up with it, since the only common factor between my home and work PCs is geographic location. Everything else like ISP, OS, Browser, Antivirus is different and tried different things where I can. It's intermittent and unpredictable