Great question! One by one:
Dgrin: Will continue to be a place for folks to share photos, talk about photography, and also ask support questions. Many questions are one-off in nature and we handle them. We also handle the routine stuff that would be great questions for Stack Exchange, too. Then there's the sticky problem about customizing, and the code behind lots of hacks, and the sometimes-very-individual nature of customizing help that's given on Dgrin. I don't think the latter will ever change, and it's not something that Stack Exchange is suited for anyhow.
http://help.smugmug.com the place for all things help-wise from SmugMug. Our official help pages. I think that many posts on Stack Exchange will reference pages on our help site. But in no way is SE intended to be any form of replacement. Also you can chat real-time with SmugMug Support Heroes via our help site.
http://news.smugmug.com - our official blog site. We make promotional announcements here, we announce new features, and we instruct here.
http://sorcery.smugmug.com - our Sorcerer's blog, a place for geeks to geek out.
http://getsatisfaction.com/smugmug - another (very little used) avenue for folks to get in touch with SmugMug Support heroes.
http://www.smugmug.com/smugs/info/ - promotional (what, where, why, how) and also news reporting about SmugMug User Groups.
http://wiki.smugmug.net/ - most stuff from our wiki has been ported to our help pages.
http://twitter.com/smugmug - a way for tweeters to get our attention as they need to - still always better to email us or chat with us, but we monitor Twitter every day and respond there as appropriate.
http://facebook.com/smugmug - big social presence, and we use it as an avenue to alert customers to site issues, new features, things on our blog, general photography topics, contests, promos, and more. Including peeks inside SmugMug. And it's surprisingly, a great vehicle for folks that want help - and so we're wired directly in from our Facebook page to our Support system - if someone posts on our Facebook page, it's shown to all heroes on duty as a support ticket.
SmugMug on Stack Exchange will become, I hope, a place where API guys will do their thing (deep dive technical issues) and also discussions around best practices and practical answers about customizing, using SmugMug, sharing photos, and printing, selling and marketing.