Text upside-down, characters rotated along baseline?

Thanks for all the answers! After doing some research myself and digging up some packages I never had used before, I also belive the input needs to be scanned charcter by character, as suggested by @egreg.

So here is a way of doing it in LaTeX:

\documentclass{minimal}

\usepackage{graphicx}
\usepackage{xstring}
\usepackage{forloop}

\begin{document}
\newcounter{idx}
\newcounter{posx}
\newcommand{\rotraise}[1]{%
  \StrLen{#1}[\slen]
  \forloop[-1]{idx}{\slen}{\value{idx}>0}{%
    \StrChar{#1}{\value{idx}}[\crtLetter]%
    \IfSubStr{tlQWERTZUIOPLKJHGFDSAYXCVBNM}{\crtLetter}
      {\raisebox{\depth}{\rotatebox{180}{\crtLetter}}}
      {\raisebox{1ex}{\rotatebox{180}{\crtLetter}}}}%
}
This is what I want to get.

\rotraise{This is what I want to get.}
\end{document}

Below you can admire the result. :)

Here are a couple of possibilities, using the facilities of the graphicx package:

\documentclass{article}
\usepackage{graphicx}

\parindent0pt

\begin{document}

Upside down\\
\rotatebox{180}{Upside down} Upside down \\
\rotatebox{180}{\reflectbox{Upside down}} Upside down and mirrored \\
\raisebox{\depth}{\rotatebox{180}{Upside down}} Upside down and raised to fit in line

\end{document}

Or you could possibly vary the {\depth} with a number.. say 0.5em to align the text with other non-rotated texts

Facebook doesn't actually turn the letters around, it just (ab)uses various characters Unicode provides (e.g. IPA characters). With XeLaTeX or LuaLaTeX and a suitable font, you can do the same:

\documentclass{article}
\usepackage{fontspec}
\setmainfont{FreeSans}
\begin{document}
uʍop əpısdՈ
\end{document}

(Compile with xelatex or lualatex.)

The actual characters used here are:

u   latin small letter u
ʍ   latin small letter turned w
o   latin small letter o
p   latin small letter p
    space   
ə   latin small letter schwa
ı   latin small letter dotless i
s   latin small letter s
d   latin small letter d
Ո   armenian capital letter vo

The quality of the output is of course disputable.