One of the tricky things about a fictional world like a RPG is that people want to believe in it, not have their suspension of disbelief or sense of verisimilitude broken. As a result I’ve heard more than my share of “but that’s not reeeeeeealistic!” complaints about one thing or another.
But really, if you do much studying of history or of the world in general – reality’s pretty fucked up. (See the previous post on spider-goats for more!)
Along those lines, here’s another Cracked article about seven people with real life superpowers. The kind that if you try to take them as GURPS advantages your GM will call bullshit on. From the more prosaic ones like super-strength to Daredevil-style echolocation.
The totally bizarre, totally irrational, and totally amazing are remarkably common in the real world. So be careful what you label as “unrealistic” in a game world – there just may be some real world examples of exactly that.
Geek Related 
There’s a funny Alt Text by Lore Sjoberg on Wired that illustrates this point – it’s called “The Sci-Fi Rejection Letter That Time Forgot” and it has an editor basically calling someone’s pitch for the cold war ridiculous. Stockpile weapons and not use them? Against human nature! Check it: http://www.wired.com/culture/lifestyle/commentary/alttext/2008/07/alttext_0730