We're really short of Mac people here - please post back if you find a solution; it could help lurkers a great deal.
Perhaps you could supply more details of your setup in case any experts happen along - Mac models, OS, whether you are connecting to a router wirelessly or via ethernet cable would all be useful.
I always find eBay is the first site to cause trouble if something is starting to go pear-shaped with my own setup. Presumably they simply try to load too much stuff for less capable equipment to handle it.
In this instance, all your computers are affected, which suggests something other than the machines or their software is causing you trouble (unless the trouble started after a recent software update, for instance, which affected all the machines and coincided with the start of your hassles.)
If you're connecting wirelessly, try using a cable instead. If things improve, this could be a useful clue.
If that doesn't help, try shutting down your router, waiting a little while (I'd guess ten or thirty seconds should let everything "evaporate" - how unscientific is that?) and starting it up again. This will probably reduce your internet speed for a few days whilst it settles down again, but might speed up individual page loading. If that makes sense.
Disabling IPv6 has helped on occasion (google for details, if necessary.)
No idea why clearing cache might help, but this is sometimes suggested when things slow. Anecdotally, eBay does seem susceptible to problems with locally stored stuff - cookies, flash cookies, whatever other junk useful elements it stores in browser cache - and sometimes clearing the whole lot and restarting your browser might help. Odd that all your computers and browsers should be afflicted at the same time, though.
If none of that helps, post back with more gen, and hopefully someone more knowledgeable will be along in the morning. Best of luck with it!
