I use gntp-send for Growl on Linux, in Rails development. Here are the instructions that I followed that seemed to work:
Add two additional software sources to your `apt-get` repositories
sudo add-apt-repository ppa:mattn/gntp-send sudo add-apt-repository ppa:mattn/growl-for-linux
Download the .tar from https://github.com/mattn/gntp-send/downloads
tar -xvf [name of the tar file you downloaded]
Install the compiler dependencies. I had to install the following in Ubuntu 11.10, but watch for error messages indicating that you need additional libraries.
sudo apt-get libtool automake ./autogen ./configure make -f Makefile sudo make install
Install Growl for Linux (this is the easy part)
sudo apt-get update sudo apt-get install growl-for-linux
Finally, start Growl manually (it doesn't appear to startup automatically)
You should start receiving alerts, if everything has gone well.
UPDATE: After using this for a few weeks, it seems that I often have to close/re-open growl after the machine sleeps, or other system events seem to happen that cause the growl alerts to stop appearing. I haven't yet looked into what the specific cause is, so I don't have any more information than that, but I figured I'd let people know that this isn't a 100% solid setup yet.
Simply running growl again seems to fix it, but it's rather annoying that it does't just work as-is.