I recently purchased a Samsung Galaxy S (the Captivate version) and I naturally wanted to be able to transfer files between it and my Linux desktop. I'm using KDE 4.5 on Kubuntu 10.04, but there are probably ways to do this using Gnome as well.
Initially I used a USB cable and configured the phone as a Mass Storage Device, but then I got to thinking that there had to be a way to use WiFi instead. Especially since I didn't keep a compatible USB cable at my main computer. After a little searching I came a across a great app called SwiFTP.
SwiFTP is a nifty FTP server that's very easy to use, but will need some basic setup the first time you use it. There is a prominent Setup button and pressing it allows you to enter a username and password. Do that, press Save, and you'll go back to the main page. Touch Start and you're in business. You'll see a WiFi URL listed that you'll need for the next step.