I work on a number of open source projects, and many of them use the Subversion version control system to manage their code. Before my switch from Windows XP to Ubuntu Linux (which I am still ecstatically happy with btw), I became a big fan of TortoiseSVN, an extremely useful Subversion client that integrates itself directly into Windows Explorer.
TortoiseSVN is simple to use, very intuitive, and does everything I need from it. You simply right click on a folder you want to store your checked out files in, give it the URL of the Subversion server, and it checks out the code, updates it, checks it back in (if you have permission), performs file diffs ….. basically everything you need to do is integrated right in with your file browser.
So, I miss this in Ubuntu, as TortoiseSVN is Windows only. However, I recently found a replacement, which integrates nicely with Nautilus, the Ubuntu file browser. While it is not as slick as TortoiseSVN, it works in a very similar way. You right click on a folder, and have a selection of SVN operations you can perform.
One thing that is missing from this is the display of icons in the file browser (Nautilus) to inform you of the state of a file – checked out, modified, not added to source control etc. Another person has developed a solution to this, which unfortunately I have not, yet, been able to get working, but perhaps you will have more luck.