About 4 months ago we took on a new developer and I started by explaining that it takes about 3 months to become confident with Plone. Being a confident developer he took this as a challenge, assuming that he would be over the learning curve within 3 weeks.
After 4 months plus of working with us I asked him to give me his feelings about my 3 month timeline. This was his response (with a few additions from me):
"I think I'm comfortable with it. However, it [depends on] the type of task you've given me... I might be uncomfortable with [doing a migration]. It's like giving a recently graduated doctor the task of performing a heart surgery as his first task at the hospital..."
So he's comfortable with some tasks but there are others that will require more experience.
I've actively been experimenting with ways of making Plone easier for at least 3 years (and less actively for longer than that). In that period I've come up with the idea of Plone Drills, created a Diazo Snippets Library and Chrome Plugin, worked out fast cloud based installation of Plone, done work on a Plone Newbie Developer Toolkit (Plone 4 only), contributed to Alex Clark's Plock Plone Installer project and spent a lot of time on a theming approach for Plone which "extends" Diazo called Gloss. I also created a short video series related to using Gloss with Webflow.
I'm still haunted by this problem space and the general idea of on-boarding web developers. It's led me to my latest side project, the aim being to provide a faster on-boarding experience for new Plone developers. I've been calling it a book but that might be a poor description since it will most likely involve more than just a text.
BTW... If you are interested in the fastest way to get going with Plone then I'd encourage you to sign up for my upcoming book/project/thing. You should see the option to sign up somewhere on this page.