Currently, only FTP download is supported by the FTP Sampler. It would be useful to have FTP upload as well. I'm actually part way through the implementation of this. I'm doing the work on company time, but if I can get my employer's approval and work the bugs out, I'll submit a patch.
Looks like there are problems with the FTP download hanging. This may be tedious to fix, so I'm thinking that the simplest solution would be to use an existing library such as the Jakarta Commons Net library. This includes an FTP client. Using this should make the addition of FTP upload much simpler too.
Fixed in SVN in r533328
This issue has been migrated to GitHub: https://github.com/apache/jmeter/issues/1922