You can import your Facebook friends into Google+ via Yahoo, but that's a fiddly process. Chrome extension Facebook Friend Exporter potentially makes shifting friends across a little easier.
After installing the extension, an option to export your contacts appears next to your Home button on Facebook. You can export contact data either as a CSV file or directly into Gmail; the latter is obviously easier if you want to add those people into Google+.
The extension seems pretty experimental right now: it only works on English-language Facebook accounts, requires you to disable HTTP, and won't necessarily work (it repeatedly hung for me just before getting through my list of friends). However, if you do want to move your Facebook community into Google+ and it works for you, it seems like an easy way to make the shift. Let us know how it goes for you in the comments. Update: Perhaps unsurprisingly, Facebook has blocked the functionality of this extension. The developer says a new version is coming; we'll keep you posted.