One thing I would recommend Andrew is, "Never throw pearls before swine."
Meaning, if you are working with or leading a group of developers who are vehemently opposed to any new technology like Ruby, Python, etc. then don't bother. It's not worth it to convince them since the threat to their jobs and ego is too much.
In my opinion, you're better off hiring a group of new folks who are interested in learning the new stuff, then a mentor to train them, and then use the previous group as maintainers. Eventually the previous group will either find new jobs, join the new group willingly and eagerly, or be happy to keep the old systems working. I think the best people for this are folks with degrees NOT in computer science who are smart and can already code.
My only word of caution is that when the old timers join the new group you've got to watch for saboteurs. I actually worked on a project where a new sysadmin got caught purposefully crashing our servers. He at first was just killing the processes and changing file permissions (Samhain is your friend), then him and other sysadmin friends would just walk over to the box and turn it off.
I worked with another guy that would spend all his free time finding flaws in RoR and then come to work ranting about them or demanding we use these features so he could demonstrate how screwed up they are.
So just watch out for this. It happens a lot more often than you think, and many times it's just not worth going to the trouble to use possible saboteurs.
Hope that helps.