It only happens from time to time but not necessarily several times a day. When the issue occurs its as if I am offline but in reality its still connected.
Like you the only solution I have found is to get offline and reconnect. Quite annoying if you have something important in progress.
Every day, often several times a day, my Internet will stop working. I'll just reload a page, and I'll get an "Unable to connect" error. Then nothing works until I restart the computer. It happens randomly. I'm still able to ping websites, though.
I'm using Windows Vista Home Premium, I connect to the Internet through a PCI NIC and to a router through the onboard NIC.