PS: I am a Hongkonger which often goes to Mainland China and I am living with two friends which are Chinese and Hongkongers who often live in Mainland China
First of all, plan on no access to Google services, not just Google search but also Gmail, and other service, even for Google Play store. Other western social media like Facebook and Twitter are not accessible.
Microsoft seems to be in the good graces of the authorities. There is no problem to access Microsoft services like Hotmail, Bing and Skype.
Most IM software are accessible in China, including Whatsapp and Skype. In China the most popular IM software are Wechat and QQ, the first one is like Whatsapp and the second one is similar to ICQ. However, Line is not accessible in China.
Actually the "height" of GFW depends on the "sensitive" day(敏感日), more website will be blocked when closer to these days, like 4th June which is the day of Tiananmen massacre. You would expect more "western" website like Wikipedia will be blocked on those days.
Finally, VPN is not 100% blocked. Many Chinese local use VPNgate to access prohibited websites. VPNgate is free but the connection is not good. On the other hand, you may purchase VPN services, which costs around 10 USD per month, depending on the speed and the amount of data.
Finally, there are some recent blog entries which may help you: