If you want to follow multiple sites at once, tag filters on stackexchange.com are one way to do that. But they have a few disadvantages over just visiting the sites directly, one of them is that they didn't get the shiny new live updates that stopped the wear and tear on everyone's F5 button.
So currently you still have to refresh the site to see if there is any activity in your tag filters, instead of getting the live refresh.
Please add the live refresh functionality to stackexchange.com. The currently selected filter would be the most important part, but updating the number of new posts in the currently not selected filters would be nice as well.