Look at that!
Simplest way to deploy a static web site, like those generated by jekyll, over ftp.
Just create a deploy.sh file at the root of your site directory:
FTP_SITE=your.site.com
FTP_USER=yourusername
FTP_PWD=yourpassword
olddir=`pwd`
cd _site
lftp -e "cd www && mirror -Re --parallel=1 -x deploy.sh -vv && quit" -u $FTP_USER,$FTP_PWD $FTP_SITE
cd $olddir
Then just type .deploy.sh and BAM, done.
Nothing fancy, nothing new, but it works and it is simple.