In Star Trek:TNG season 2 episode, Up the Long Ladder (the one where they have to evacuate the colony of clones and the colony of Irish farmers), Geordi reveals that, using his visor, he can tell when humans are lying to him. This seems like a very useful talent. Did they ever mention this again? Or are there specific instances where Geordi should have been able to detect a lie, and didn't?
Most of these early super powers were not addressed later in the show. If you think about it, having one character that can read emotions and another that can detect lies and just about anything else really make writing stories hard. Every alien race that you meet ends up being completely transparent and obvious to your team, so in order to deceive they would all need to have some cheap plot device to be able to avoid being detected.
Not only that, but you'd have to think up a new way to best them each week. What will we use this time? A lie-enhancer ray? A field of lying? A charm spell?
Combine all the silly things they used to prevent Troi from reading emotions, and now increase that to include nearly everything a body can do.
In universe, we can assume that his power was exaggerated and isn't as amazing as he let on.
While not mentioned again, Geordi is, throughout the series, apparently able to tell when Wesley isn't being honest, pushing for more information gently.
It's no super power, anyway; given that his visor lets him see in a wider spectrum, including IR, he would be able to notice changes in blood flow readily. Further, if focused upon a person, he's able to see much smaller details, so he'd be able to focus on pupil dilation. Given those two, there's about 1/4 of a full polygraph test.
It should be noted, tho', that he's not going to be all that much more accurate than a polygraph, either... and polygraphy is only about 50% accurate.
There's at least one other instance where Geordi successfully detects a lie by looking at someone with his VISOR, in TNG: The Enemy.
[Bochra's head weaves momentarily as though he's dizzy.]
GEORDI: What's the matter?
GEORDI: Wrong. Your heart rate just shot way up.
[Bochra can't help his curiosity, looks at Geordi -- How can you tell? Geordi taps his VISOR in response.]
GEORDI: It translates a wide range of radiation into neural impulses. Allows me to see.
By comparison he fails to see multiple people lying to him in TNG: Starship Mine although perhaps he's more interested in the weird about-to-explode table to fully notice.
ORTON: (smiles) I'm sure we can handle this, whatever it is, Commander. There's no need to concern yourself.
GEORDI: I really think I should look at that heating element. If it overloads under --