Liar's Pendulum looks like a gimmicky draw engine that trades a cheap cost (both to play and activate) for an unreliable return on your investment. I mean, it's not the most reliable way to double your resources, earning what should be a 50/50 chance of drawing another card each turn, but sometimes that's not what it's all about. This is a very interactive; very fun card.
Let's say you're holding a counterspell in hand and name it. If your opponent guesses no, you can either take the extra card OR just refuse to show your hand and skip the extra draw. At this point your opponent should probably assume you aren't holding a counterspell and play accordingly, allowing you to stop whatever key card he's been sitting on for fear of countermagic. If he guesses yes, however, you can show him your hand and force him to try and play around it (and remember, you might draw a second counterspell before he makes his move) or simply refuse to show it and see if he calls your bluff. Either way is a plus for you, and either way you're playing another game within the game.
Liar's Pendulum isn't a rock steady card engine like Jayemdae Tome, but it's instead designed to let you bluff your opponent into playing based on what he thinks is in your hand - a key component of many control decks, but in this case you can actively influence it. If you score extra cards, that is great, but even if you don't, you still come out okay. Just remember that the Pendulum says you MAY reveal your hand - if you think you're better off keeping information to yourself, you don't have to.
