ftp insecurities?

[imtiedup]

I was told by my host that ftp is very insecure and I should only have sftp on my server, and I wasn't going to argue with him as being the network engineer at the datacenter itself, I figure he knows what he is talking about,

So, I find a program today that I purchased, that only connects to my server via ftp, and not sftp. I asked for sftp, he said someday, don't worry about ftp. I told him ftp was insecure and had problems...

Well of course he asked what problems, and I can't answer him, left me feeling quite stupid for saying something I can't back up.

So I want to learn...

Can anyone point me to articles as to why ftp is not secure enough and why not to use it?
*bonus for anything showing what people are doing to attack it (I don't mean tuts, I don't care about learning how, just why)

thanks so much for any help offered.