Not only does it require a lens between you and the object, but it requires a lens behind the object as well.

"Among the many misdeeds of British rule in India, history will look upon the Act depriving a whole nation of arms as the blackest."

        - Mohandas Gandhi, an Autobiography, page 446.

Five years ago we got my niece a Dell Vostro 1500 (the business version of the Inspiron 1520). It was getting really long in the tooth and she was considering getting a new laptop. After doing a little research I discovered that the Vostro 1500 is one of the most upgradable laptops out there. Using a combination of craigslist, newegg, and amazon I was able to perform the following upgrades for a total of $203:

Battery: 6-cell -> 9-cell (the old one had died long ago)
Storage: 5400RPM HDD (160GB) -> SSD (90GB)
Memory: 2GB -> 4GB
CPU: Intel T5270 @1.4GHz (65nm) -> Intel T9500 @2.6GHz (45nm)
Optical: DVD/CD-RW -> DVD-RW

I could have added bluetooth, a blu-ray player, or even upgraded the graphics card (!), but there was no pressing need (and I was trying to stay under $200). My goal is that she gets another two years out of it.

I guess my point is that, even though some of these upgrades aren't for the faint of heart, upgradability is something to consider.

if i RTFA correctly, by 'limited turing test' they mean to see if any second-lifers fail to notice that there's a bot in their midst; that's been happening for a long while now (e.g. Barry's fateful encounter with Julia on TinyMUD).

if on the other hand the occupants know there is a bot in their midst, determination will be trivial to achieve and impossible to prevent:

"hope you don't mind if i start typing everything backwards... ?eman rouy s'tahw os"
"c4n u r3ad this @nd r35p0nd |n p|g l@t|n?"

etc.