Kind of an expensive "splurge" item (as low as approximately $18-25 per person), but seems like a good deal - if you're looking for something like this. Read on ...
Here are the steps for maximizing this deal ...
1) Check your email (especially if you've ever shopped with Amazon, or especially/specifically Amazon Local - which is Amazon's "Groupon" sort of website). Search to see if you got an email from Amazon Local in the past few days with a subject line of "20% off sitewide. If you did, then this deal is even better (half-off or a little better). If not, then skip this step and you'll still get nearly half-off. THIS DISCOUNT IS ONLY GOOD THROUGH January 10th (but the voucher for going to the buffet at Portland City Grill is good for any Sunday over then next 90 days). And I'm not sure how long the voucher itself will be available (in step #4, below, you'll see that the website simply says "limited quantities available" - so not sure how long this deal will be around).
2) Go to a new/clean (preferably incognito) browser, where you haven't recently "surfed" to Amazon or Amazon Local. Go to TopCashBack.com (if you've never been there or signed up for a free account there - please consider using my affiliate link HERE). Search for Amazon Local, and click through to Amazon Local from there (after you sign up for an account) and you'll earn an extra 6% back on your purchase.
3) If you have the email from step #1 (above), go back to that email and click through from the link in the email for the 20% off.
4) Now at Amazon Local, search for "Portland City Grill." You should see their two buffet options (with and without mimosas), with the cheaper one being $50 for two Sunday buffets (regularly $78). A pretty decent deal on its own (for what sounds like a nice buffet - with pretty good reviews on Yelp). But a really nice deal if you get the 20% off (and everyone can get the 6% cash back from TopCashBack).
As I mentioned (above), the voucher is good for 90 days. The important thing to remember about these type of vouchers (including Groupon & LivingSocial) is that if you forget to use them in the "promotional" time period (90 days in this case), the vouchers do NOT become worthless. You can always use them for "face value" (what you paid) at the merchant (or else Amazon or Groupon will give you a refund).
Unfortunately, the fine print says maximum of one voucher per table, if you're looking to take more than 2 people. But I think that you can sometimes by $100 in "Restaurants Unlimited" (Portland City Grill is one of their restaurants) gift cards at Costco for $80 (or $90?), in case you're looking for a discounted way to take more than 2 people. You can also buy those gift cards online (in various denominations) at various places (use GiftCardGranny.com) to look up the cheapest place to buy them.