Hey Jared,
I'm literally at this moment doing a bunch of research for latest examples and best practice for this with an upcoming project, and was thinking about posting a similar question 
Found this to be a really interesting read thinking about UX design philosophy around the customer facing components of it: https://medium.com/stack-overflow-design/designing-a-better-email-preference-center-4fddd44b91b5
Overall, my basic philosophy really boils down to this:
Keep it simple & clear:
- Make complete unsubscribes clear and accessible. We can try to provide them with other solutions, but if they really do want to unsubscribe, make it easy for them.
- If you're going to give people the option to opt out of particular types of emails, choose categories that are meaningful to them, be clear about what those categories entail. Be as high level as is meaningful, go as granular as is meaningful (emphasis on to them). No more, no less.
- If you can, create a consistent email calendar. It helps you develop internal schedules for developing campaigns, but also makes it easier to set expectations and define clear categories for emails. E.g. newsletter is always the 1st monday of the month, promo emails are always the 3rd monday of the month. Community updates are every wednesday morning. etc.
Follow through:
- If you're going to give people the option to mute emails for a period, or control the frequency of the emails they receive, make sure you implement an automated process to do and then undo that.
- Remove the human element as much as you can. Create master lists for the audiences for different comms, develop clear processes & automate them as much as possible. The preference centre is pointless if you don't honour it, and making as many steps automated/templated as possible reduces the risk of human error.
- If you set an expectation around frequency and timeframes, stick to it.
So far as issues I've seen - it's really stuff that influenced the above, mostly options being given but not honoured in send rules, and lack of clarity in design, where people would untick all the options except the actual unsubscribe. Because people weren't honouring the preference categories, people who thought they'd unsubscribed were still receiving emails.
Keen to hear other thoughts 
Hey Jared,
Having just launched ours, I learned a few things.
- If you have multiple companies (not brands) using the instance, it's very difficult to create a reliable unsubscribe system outside of marketo's built in unsbscribe field and system
- With that said, I'd recommending using use the default unsubscribe functionality to manage full unsubscribes.
- Preferences are fields in the account and if there are *duplicates* of that lead, you need a way to pass those fields to the duplicate account (if someone is partially unsubscribed and their dupes don't have updated preferences they will receive those emails)
- If you need to comply with GDPR, you'll need to find ways to identify their state of subscription as well as update consent types if they change their subscription status (also unsubscribe date)
- You'll likely need to use some javascript on your landing page to ensure that if they full unsubscribe that their preferences are completely cleared (theres a lot of cool things you can do with javascript such as give them their subscription statuses after they update them)
- You'll also want to set up some very clear smartlists for your email blasts - unusbcribed category = false, email invalid = false, unsubscribed = false (what we use for best deliverability)
- If you run webhooks you'll wanna create internal alerts in case they don't fire correctly. Your webhooks should not be critical to the functionality of the actual system - if they misfire they should be easy to catch them up.
If I think of more I will add them
.png)