Even if we concede to the magical thinking that XKeyscore will never be used against an American...

[Benton D Struckcheon]

16. Didn't really look at those slides, didja?

Across the top it lists other countries with whom we are running this intelligence: Canada, Great Britain, Australia, and New Zealand. Might be one other that I'm missing.
Anyways, point is, the idea that foreign govts aren't doing the same thing is just hopelessly naive. You are less than the dust beneath anyone's chariot wheels anyway, they're looking for trade secrets, official intelligence, all that kind of thing.
As for who might be looking for you, well, that would be Facebook and all the rest, but you already knew that, I'm sure.
Oh, and by the way, here's that eehhvulll PRISM:

With the rise of social media, more and more individuals and organizations are posting publicly available content.Within that content lies pertinent information which is useful to organizations. Before PRISM, users had to manually comb through multiple social media sites to try and synthesize the available data for information relevant to their needs. PRISM offers a single place to pull together all available data, filter out the noise, and make sense of the avalanche of information out there. To aid users, PRISM features the ability to map posts, compare digital footprints, monitor profiles, and to identify and monitor organizations. Users can export all data, including meta-data, for use with knowledge visualization analytical tools. PRISM is built upon an extremely versatile platform which can be accessed from anywhere with an Internet connection. PRISM allows any organization to efficiently manage the collection and analysis of publicly available information on persons, organizations and events.

I remember reading in some book by a former spook, don't remember which now, he said the first thing in their routine was to do the "checkables", that is, all the stuff that's publicly available about your target. Said there was a ridiculous amount you could find out just from doing a thorough job with that. That, it appears, is what PRISM does for the spooks. And not just them. Note that it's available to any organization, public or private, that wants to aggregate publicly available info and create a database of it for whatever purpose they have in mind.
So, given that, and given what can be found out about you from what you post here and elsewhere, well, I can't for the life of me come up with a reason for why the ordinary person cares about what Snowden "revealed". If you were really going out on the Internet thinking what you posted was going to be private, well, I don't know what to say. Foreign govts are already hacking into everyone else's networks, but they're not looking for you. The folks who are interested in you are using PRISM and other very similar tools to put all your info into a massive database the better to sell to you their stuff, or maybe check who you are before they hire you, all that kind of thing. None of which should be news to anyone.