If you wonder how the past 12 months went by so fast, Twitter and Facebook may be able to help. The two social networks have separately launched apps that generate a personalized report — think of it as a solipsistic version of the annual Zeitgeist report Google just posted – that tracks your activity on each service.

I like this idea. A lot.

For one thing, it's not like social networks haven't been analyzing all this data for the benefit of their advertisers already. For another, you might learn a thing or two about yourself from looking in this software-generated mirror.

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Twitter launched its "Your Year on Twitter" option on Tuesday, as part of its year-end recap. This feature comes from a third party, Portland, Ore.-based Vizify, which requires you to let it peek at your account (Vizify only asks permission to read your tweets, not post new ones for you) and limits its reach to your last 3,200 tweets (all that Twitter permits other apps).

As a result of that latter issue, my "Year On Twitter" report only covers from August on. In that time, my top topic was "#demo2012," the hashtag for the Demo conference I covered in October, followed by "app" and then "phone."

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My most-retweeted "Golden Tweet" was a snarky political comment about CEOs who had threatened mass firings after an Obama reelection. And my "Golden Follower," the one who mentioned me most often, was Seattle-based tech journalist Glenn Fleishman, who is sufficiently active on Twitter that his own report probably only spans the last two months.

Facebook debuted its own year-in-review feature Wednesday morning (followed by news of some upcoming, useful tweaks to its privacy interface). This summary, available at facebook.com/yearinreview if you're signed into your account, highlights "your 20 biggest moments."

But since that list includes not only your own updates and photos but posts from others in which you're tagged, it can be skewed by input from tag-happy friends. Most of my own highlights involve news about my daughter (probably the case for every mom and dad on Facebook), with posts about the Washington Nationals taking second place.

It's also useful to know that I added 34 friends and liked 5 pages, but it would be more helpful yet if Facebook would total how many people I unfriended and pages I unliked. I also hope that next year's version reports which Facebook friends I interact with most often.

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Other social sites would do well to follow this example. Some already offer this data but only do so monthly: Google can send you "account activity" statements detailing your use, and Foursquare provides statistics about where and when you check into real-world locations on that service.

In some cases, outside apps can do the extra math or provide added details. I used Vizify to generate a Foursquare report, as seen in the restaurant breakdown in the image above. And the AwayFind mail-management service I'm trying tells me how quickly I answer frequent correspondents; for my usual editor at Discovery, it's 41 minutes.

The more curious or obsessed among us could then mash up all of this data into the kind of hyper-detailed "personal annual report" that writer and Facebook designer Nicholas Felton has been producing since 2005. (Sample minutiae from the 2010-2011 edition: "Most Visited NYC Shops" and "City Visits Restricted To Airports.")

But you wouldn't have to go that crazy with the "quantified self" ideal to get some worthwhile insights about what you're doing — and shouldn't be doing — with your online life, if only more services would tell you about yourself.

Credit: Rob Pegoraro/Discovery