When I first get on the internet I check 2 emails, ebay, 3 forums, 2 discount sites(hotukdeals and moneysavingexpert for any bargains). I start with the emails, once checked I close those tabs, I check ebay for any messages and to see if anything is ending then close that tab. I check the discount sites and close them. The 3 forums I check one first as it usually only has a dozen new posts, checked.. tab closed. That leaves me 2 tabs / 2 forums that I flick between as I read the hundred or so new posts, hardly ever replying.
I also sometimes open a site like failblog to amuse myself or some sort of retail site to browse and rarely buy from. Right now the only tab I have is WP but I'm thinking of doing my daily search for ridiculously cheap PS3 games on ebay or game retail sites.
I think the most I ever have open is around 10-12 and that's when I'm looking at many retail sites if I'm intending to buy something and want to find the cheapest price. Example being yesterday I was looking for a new PS3 controller I had 2 game sites open, ebay and several other retail sites.