Just be careful using FTP when mobile, especially over WiFi when anyone on the network can see the FTP username and password even if it is a secure WiFi network.

I have Mobile Me and have some files on the iDisk and am using an app called MobileFiles which is pretty good for accessing them from the iPhone. Dropping some map images or reservation PDFs into your synced idisk folder on your mac is a bit easier than emailing them to yourself.

(SEE DISCLAIMER AT BOTTOM)
There are other option to do this too. CrushFTP is server software providing FTP, HTTP, HTTPS, and SFTP server functions. CrushFTP can run directly on any machine, and serve out the files. You can use HTTPS from the iPhone to access the CrushFTP server you run. No need to configure a FTP server, and another app to provide HTTP access to that FTP server as this hint detailed.

The WebInterface of CrushFTP works well with the iPhone too.

However, if you wanted to go that route, there are a lot of options you can do via Crush. You can share out other FTP server's directories to the CrushFTP server's WebInterface. So a remote FTP site looks just like a local folder when you are browsing the WebInterface.

You can apply the same principal for SFTP servers...have Crush provide a HTTPS WebInterface front end to the SFTP server.

There are even more complex and powerful things you can do as well...such as configuring a user definable proxy mechanism for CrushFTP. This means you login to Crush, then enter the FTP site's info, (ip,user,pass), then click next and crush dynamically builds a WebInterface to that remote FTP site on the fly for you. You can even have presets created too...so its good for an organization with many people doing this.

CrushFTP is highly customizable, and does things no other server can do. These are just some examples of how it could do what this tip was about...but do it in about 3 minutes of setup time. If you want more info, email me.

Disclaimer: I am the author of CrushFTP, and stand to make money in the event you purchase it. ben@crushftp.com