I have to deal with lies everyday. It's called work.
See, I work at Hastings, which is a retail chain selling books, music, movies, software and various sundries. Well, the magazine department falls in my work area. While on shift, I routinely patrol there, pulling adult magazines that have been taken out of their protective slips. Often, I'll see someone 'browsing', so I'll point to our little sign which says "We ask you not to remove magazines from their green bags.", verbally state this, then wait for the reply, which invariably is, 'I didn't take it out the bag...it was already there like this.' I love hearing that when I've gone through magazines and looped back after about 5 minutes to find some guy reading another adult magazine when he thought I wouldn't be around. Go fig.
Now, as for relationships or friendships, when lied to, I put the offending person on a mental list. If I see this behavior becoming a pattern, I write them off. For gross offenses, they are Personae Non Gratia. I make it a point to inform them of this and why, then I go about my way. I just don't have the time to bother with people like that.