a 3 letter .info just sold at around 15k or something like that on sedo. At wholesale 3 letter info's pull around $20-40 Retail can bring in a whole lot more but is often rare. 3 letter .us have a wholesale value of about $5-10. The value depends on the combination of the letters and also who you are trying to sell it to.
How come I NEVER see anyone offering 3-letter .us domains at $5-$10 wholesale (without q,x,y,z or j,k,u,v in them)? I would buy a TON of them in that price range if anyone would offer them.
There are more people now than ever using the internet and this translates into more names being sought. I say grab up all the 3 characters you can find becuase the value of .us, .biz, .info and all the other dots are growing at a faster rate than .com did a few years back. The internet is still growing!