I have had intermittent problems connecting to the internet on my TC, but have managed to piece the solution together.
This may help some people if, like me, you could connect to a network but not access internet pages, or only occasionally access them.
I discovered that my TC was not using a correct DNS address or something. I was getting "host not found" error messages. I opened up my network settings page on the TC and changed DNS address from automatic to manual. I found my DNS address from my router's control panel (Belkin router) and simply put the numbers into my TC.
Now it works fine. It seems that the TC has trouble automatically getting a DNS address.
This may not address the problems that most people are having, but it may help some people out there!