http://en.wikipedia.org/wiki/Kitchen_knife#Utility
"A utility knife is between a chef's knife and paring knife in size; generally too fragile for heavier cutting tasks, and not well suited to fine tasks, the utility knife has declined in popularity. They are usually between about 10 cm and 18 cm (4 and 7 inches) in length."
I was taught to cook with the chef Knife, utility knife, and pairing knife. The utility knife I prefer is 6" in length, and good for trimming fat off lamb and chicken. Although it's not as strong as the chef's knife, it's still good enough to cut lamb into 1" cubes. IMO the chef's knife is too large for some jobs and the pairing knife too small, so the utility knife fits perfectly in between:

Wüsthof sells the knife as the "Classic 6-Inch Sandwich Knife", they also have a 6.3" utility with hollow edge, which I don't like because I prefer classic blade style and handles.
So I walked up to the store's knife counter and asked to see the 6" utility knife. Lo and behold, I get a sales guy who insists that there is no use whatsoever for the 6" knife and, in his opinion, I have no reason to buy one. I explained that I prefer to have a medium knife in my knife block, and he demanded that I justify myself for buying such an useless knife.
Uh, excuse me? Hello? I'm the customer and you're the sales guy?
This is the typical American as*hole behavior where people don't appreciate you for buying something from them, or giving them advice for free. Instead, they want to argue and demand that you convince them that your suggestions or opinions is superior.
Hey as*hole, I'm doing you a favor for just stepping into your store. Which idiot hired you anyway?
Many thoughts went through my head. I could stand there and argue with him, ask to speak to another sales associate, complain to the manager... but what's the point? If he thinks it's a good idea to bitch-slap customers, then he's not going to last long at the job anyway.
So I said, never-mind, and voted with my feet -- I took my business elsewhere. F*ck off, adiós.
I took my business to Chef's Toys:
http://www.chefstoys.net/
I told the guy at the counter what happened at the other shop, and he just shrugged and said "you're the chef, you choose whatever knife you want to use".
Now there's a man who speaks my language.