Unfortunately (for me at least) Pandoc isn't yet a standard package in Ubuntu Gutsy (it will apparently be in Hardy) and as far as I know, it hasn't been officially backported.
So, I had to install it myself, package by package, finally compiling from source:
First, version 0.46 (and 0.45) had an error that prevented me compiling it:
./setup configure --prefix=/usr/local --with-compiler=ghc --with-hc-pkg=ghc-pkg
setup: pandoc.cabal:39: 'Executable' stanza starting with field 'library
make: *** [dist/setup-config] Error 1
I was able to successfully make version 0.44 by first installing the following packages from the usual (Gutsy) places:
jkemp@deepsea:~/$ sudo apt-get install ghc6 libghc6-xhtml-dev libghc6-mtl-dev libghc6-network-dev
Note: I determined the necessary libraries by checking the pandoc.cabal file included in the source tarball, and adding 'libghc6-
After doing that, and unpacking the source tarball, I just ran 'make' and 'sudo make install' in the source directory, and voila, I was able to run Pandoc!