I have 2 friends (and 2 acquaintances) who joined the Peace Corps... and all I can say is that it definitely changed them. :/
It's probably a positive experience in the grand scheme of things... but the most common thing I've noticed is that none of them are as lighthearted as they used to be. They act more serious, more moody, and more annoyed by things... (which is probably because it's hard to go live in Africa for 2 years, where you have to walk for 8 hours to retrieve some water -- and then come back to America, where people are complaining about the long line at Starbucks or having to stop at a stop light.
)
But I've talked about it in depth with two people, and they both really enjoyed being gone. One of them actually came home for Christmas, and ironically: she couldn't wait to go back.
I think it would be hard to adjust to the lack of luxuries... like the way that they don't have cell phones, or the internet, or washing machines, or big fluffy beds. But I think the hardest part would be
not having any income and being away from your friends & family for 2 years. :/ (You don't get paid for going; you just get a small monthly stipend.) That would be rough. But I'm sure that it's enlightening, and challenging, and humbling.
I can't remember the names of the specific programs that they were involved in...but I can ask them and get back to you.