Based on the open source intelligence available, we have to assume that governments all over the world are constantly monitoring the activity of their citizens online, for reasons both reasonably benign and exceedingly nefarious. It is worth remembering that even if the official purpose of a surveillance program is acceptable, it can be abused by anyone who gains access to it for purposes that may be very dubious. Hackers and rogue government agents are well positioned to use internet surveillance to rob or blackmail people, for instance. It is also worth remembering that data is not only being monitored in real time; it is also being archived for unknown future purposes.
Tools for privacy
Thankfully, we do have some tools to make this ubiquitous surveillance more difficult to carry out. You probably cannot encrypt your hard drive well enough to protect the contents if government agents grab it, but you can encrypt your online communications sufficiently well to make it at least challenging to decrypt them. The more people streaming gigabytes of data via encrypted HTTPS connections, the less feasible it is to archive and crack internet traffic taken all in all.