After having read this post yesterday. I feel like that was my turn to put my 2 cents. After some tests, I tweeted the javascript code below which return "boNjour":
$=-[$=[]],$$=$/$+(!$+{}),_=-~-~-~$,__=$$[(_*_)+~$],$$[_*_]+__+$$[$]+$$[-~(_*_)]+__+$$[_+-~-~$]+$$[_+-~$]

How ? Where are the letters ?

The first statement is:
$ = -[$=[]];
$ == 0
With this $ I can get all the letters I want for the word "bonjour" thanks to the second statement:
$$ =  $/$+(!$+{});
$$ == "NaNtrue[object Object]"

$/$+(!$+{}) ?

First of all, I wanted an n:
$/$ == 0/0 == NaN
typeof($/$) == "number"
Next an u & r:
$          == 0;
!$         == true
typeof(!$) == "boolean"
And finally the b o j:
true+{} == "true[object Object]" // Thanks to type coercion
!$+{}   == "true[object Object]"
Then, I needed to convert NaN (a number) to a string. Which is easy with javascript's type coercion:
number + string = string
So:
$/$ + (!$+{}) == "NaNtrue[object Object]"
$$ = $/$ + (!$+{});

The last statement of the code do the following:
$$[9]+$$[8]+$$[0]+$$[10]+$$[8]+$$[5]+$$[4] == "boNjour"

But... where are the numbers ?

The NOT operator is the anwser !
The ~ operator in JavaScript means -(N+1) so -~ = +1
if $ = 0 then -~-~-~$ = 3

Remember, we already have 0 (with $):
$ == 0
I started with a 3, because 3*3 = 9, (3*3)-1 = 8, (3*3)+1 = 10, (3+(1+1)) = 5 and 3+1 = 4. We can get all these numbers by playing around with $ & ~ :
-~-~-~0 == -~-~-~$ == 3
_ = -~-~-~$
Let's do it !
_*_ == 9
$$[_*_] == "b";
o is used 2 times so it has his own variable __ in order to reduce the code's length:
(_*_)+~$ == 9 + -1 == 8
__ = $$[(_*_)+~$];
__ == "o";
$$[0] == "N";
$$[$] == "N";
1 + (_*_) = 1 + 9 = 10 //With N=9, -(N+1) = -10 so
~9 == -10
-~(_*_) == 10
$$[-~(_*_)] == "j";
3 + (1+1) = 3 + -~-~0 = 5
_ + -~-~$ == 5
$$[_+-~-~$] == "u";
3 + 1 == 4
_ + -~$ == 4 // N=0, -(-(N+1)) = -(-1) = 1
$$[_+-~$] == "r";
And here we are:
$$[_*_]+__+$$[$]+$$[-~(_*_)]+__+$$[_+-~-~$]+$$[_+-~$] == "boNjour";

Your turn now :)

[Edit] Some converters already exists:

• Convert JavaScript to strings only containing »[]()+!
• Encode JavaScript to Japanese style emoticons