For all the talk of how doing a PhD is terrible, friendships in a college-like environment after undergrad was a bright point for me and many others. I moved and started a 9 to 5 last year and it's quite a change in lifestyle, and at 30 it's striking to start to deeply understand this same life transition many friends from high school and undergrad experienced 7 years ago already.
If possible, try to time it with your closest friends because otherwise you'll rapidly run out of both 'lifestyle in common' and time.
(Tangentially: I've been thinking a lot about the theme of 'lifestyle in common' ever since both my parents and in-laws have retired and almost instantly assume that, because they can schedule 100% of their day, that we can too: my mother organised a family gathering for a Tuesday lunch - "Mum, I'll be at work, in the city, and the kids are at school...". This extrapolates in interesting ways as well)
On the flip side, when you have kids suddenly every other person you've ever known with kids of a similar age will come out of the woodwork to say hello. :)
