Facebook is a great service that I've been using for a while now, but it loses to Twitter for one simple reason: Whatever my friend Rick Munarriz may tell you, Facebook stinks at delivering ads.

Not quite adding it up
Some of the ads that appear on my Facebook profile page are perfectly fine. One, from Bank of America (NYSE:BAC), offers me business-banking services -- not bad, since I'm a self-employed writer. Another, from Target, asks that I help decide which causes will receive a portion of its corporate largesse. Also not bad, because I have the "Causes" application attached to my Facebook profile.

Sadly, these are the exceptions.

Other ads ask me if I'd like "auction leather furniture" or advice for buying a fixer-upper home -- nonsense, since we've been in our current house for 10 years. Still other ads are regionally appropriate, aimed at me because I live in suburban Denver, but the content is off: I've no doubt David Byrne is a genius, but I never was and still am not much of a Talking Heads fan. You'll find none of Byrne's work in my iLike feed. So why is Facebook pitching me to buy tickets for a local appearance?

Hey! Buddy! Can you spare $4?
If it sounds like I'm asking Facebook to know me, it's because, well, I am. The brand promise of Facebook -- its raison d'etre for delivering pitches -- is that it really does know me, in a manner reminiscent of Amazon.com (NASDAQ:AMZN) and Netflix (NASDAQ:NFLX) and their recommendations engines. My connections and content choices weave a mosaic of valuable insight that's worth something. (At least $4 per profile, at last count.) But as my experience shows, Facebook is grasping at straws about what to show me far too often.

Google (NASDAQ:GOOG) doesn't have this problem, because it doesn't really need to know me; it only needs to know what I search for. Facebook has a higher hurdle to clear. Add what Facebook knows about me to a more classic search engine, and it could lead to something special. At the very least, it'd be closer to the social-search brass ring that Microsoft (NASDAQ:MSFT), Yahoo! (NASDAQ:YHOO), Ask.com, and AOL have been chasing.

Socially stunted
Thus far, hopeful experiments with social search have failed. Google tried linking up with MySpace, only to abandon the deal when it fell far short of expectations. Said Google's Sergey Brin of the tie-up a year ago: "Monetization work we were doing [at MySpace] didn't pan out as well as we had hoped."

Perhaps that's an unfair comparison. News Corp. (NYSE:NWS) recently booted MySpace's founders in favor of a Facebook refugee, Owen Van Natta, the company's former chief operating officer. Can you blame them? There's a pedigree that comes with building one of the Web's fastest-growing properties, now 200 million users strong.

And yet Facebook's once-vaunted valuation is collapsing, even as Twitter's is reaching for the social stratosphere. Once thought to be worth just $150 million, Twitter added $100 million to its valuation in a month, stiff-armed a $500 million bid from Facebook, and is now reported to be entertaining a $700 million cash bid from Apple (NASDAQ:AAPL).

Why all the interest? Because Twitter, at a fraction of Facebook's size, is the Web's most relevant, searchable source of conversational intelligence. Entire businesses are being funded and built upon its platform.

Twitter, in other words, is already what Facebook hopes to be.

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Tim had stock and options positions in Apple and Google at the time of publication. Check out Tim's portfolio holdings and Foolish writings, or connect with him on Twitter as @milehighfool. The Motley Fool is also on Twitter as @TheMotleyFool. Its disclosure policy finds it hard to twitter while jittering. Stupid caffeine.