I had issues with Avast 7, where connection was working fine after hours I couldn't access any site. I later tested Avast on and off and it was the cause of my problem. I decided to use MSE, but it's extremely minimal which is excellent for users who don't want to deal with it or for users who want something simple. Apple has a history of claiming that their products are simple that has allowed them to be perceived as better products by the consumer population.
Now that a new version is release maybe it will work for me (Using win8) I just love hanging out in SF more.