If you aren't sure, you will soon be able to download a tool from Google that will tell you once and for all if they are. If ISP's aren't going to tell their users exactly what is happening with their network connections, Google wants to make sure that these people have the ability to tell for themselves. This announcement is Google's most recent attempt at raising awareness about net neutrality.
This isn't the first time someone has made software to monitor your network to figure out if your ISP is doing anything fishy, NNSquad Network Measurement Agent is a tool that does exactly that already. In fact, this might actually be the tool Google is referring to. Vint Cerf, Google's chief Internet Evangelist, is part of the NNSquad already.
It's unclear what kind of effect something like this will have on the network neutrality debate, but it certainly can't hurt.