Yeah. Obviously. But Harris goes further than what many people mean when they say "it's wrong to lie," arguing that even seemingly justified forms of lying, like little white lies, lying to protect someone, and false encouragement, are all wrong in their own way.
He's convincing, for the most part. Take false encouragement; the lies we tell without a second thought, like "yeah, I love your blog, you are such a good writer." It seems harmless, and it would be awkward to say otherwise to someone, but Harris makes a good point: "False encouragement is a kind of theft: it steals time, energy, and motivation a person could put toward some other purpose."
I've always been a big believer that the truth is the fastest route to success, both on a societal level (hence my interest in science) and on a personal level. It would be easy to get carried away with this, becoming one of those people who spouts his opinion whether asked for it or not, and is rarely invited to the next party. However, I think it is possible to tactfully express the truth whenever asked to.
I appreciate blunt people. Others may not, but even they can be served well by the right kind of bluntness. If I tell you that yes, you actually do look like a giant turd in that brown dress (like really, brown dress? What were you thinking?), it might hurt at first, but when you show up to the party in a different dress and get genuine compliments rather than awkward false encouragement, you're better off in the long run.
Harris also makes the point that lying is not only harmful to the people being lied to, but taxing for the liar. Keeping up a lie takes a lot of mental effort, since the lie was fabricated in the liar's mind. Every time the lie comes up, the liar has to check against his memory of previous lies, who knows what, how the lie affects everything else; he essentially has to store a new version of reality entirely in his head, often in real-time. When the truth comes up, though, it's easy to keep track of; the truth-teller only has to keep track of one version of reality. The real one.
Many of these examples assume the people involved are regular, sane people, who ultimately just want to get along. Where Harris starts to lose me is when discussing situations where this arrangement breaks down. He discusses a hypothetical situation of a murderer showing up at your door looking for a little boy who you are sheltering. Should you tell the murderer the truth? Harris argues that lying could have unintended harmful consequences; the murderer might go to the next house and murder someone else, or at best, it just shifts the burden of dealing with the murderer to someone else. Instead, a truth like "I wouldn't tell you even if I knew," coupled with a threat, could mollify the situation without a lie.
I'd argue that, when facing someone for whom cooperation and rationality have obviously broken down (e.g., a kid murderer), sometimes there are known consequences of lying (e.g., saving a kid's life) that are almost certainly less harmful than far-fetched unknown consequences. Harris later makes this same point on a larger scale, when justifying lying in the context of war and espionage, saying the usual rules of cooperation no longer apply. I think blowing up a city with a bomb and stabbing a kid with a knife are both situations where cooperation has broken down, and both situations where lying can be a tool used in good conscience.
There are no absolute moral principles that work in all situations. Life is too complicated for that. Trying to summarize it in simple prescriptive rules (as many religions have) doesn't work. So, the rule "lying is always wrong" can't work. There are extreme situations where the rule breaks down.
Luckily, most people will never encounter such an extreme situation in their daily lives. This is where Harris's main point is spot on: we should lie a lot less than we do. If everyone told the truth in every normal situation, relationships would be stronger, and people would be happier and more productive. I've certainly been more aware of my honesty since reading the book, so it's fair to say it literally changed my life. That's certainly worth the $2.00 it costs (buy it here). No word of a lie.