You can download the .deb I've created using Andrew Starr-Bochicchio's packaging from HERE.
Once installed, log out and log back in for Unity Reddit Lens to work.
For more info (like configuring it - you must edit a file for this), see the article on WebUpd8.
Ubuntu 11.10 & 12.04
For Ubuntu 11.10 & 12.04, the Reddit Lens may be installed as follows:
In a terminal, type the following commands:
Then log out and log back in to activate the lens.