If you're doing affiliate websites or you don't mind the churn and burn approach, PBNs can still be effective.
If you're looking to rank a website or build a brand around the name then I'd recommend following James' advice.
Marin is good for search. Display and social I've found it quite weak.
Display - DBM but the last time I looked at it they were charging in the teens. If you're using the GDN I've found the DCO's consistently beat Marin bidding for direct response.
Social I think the best I've seen is Nanigans.
I use it but like you I've also moved sites in the past without using it and it's worked well.
I think for the 2 minutes it takes it's probably a good idea.
Long time lurker, first time poster.
I've been involved in online marketing (SEM/SEO/Affiliate/you name it) for about 5 years now although I've only started playing around in the .com.au space for about 18 months.