I say "today only*" because similar deals from Groupon come along frequently. But this one is about as good as it gets. Read on for more details and some ideas of things to potentially buy in PDX ...
Groupon runs 10% to 20% coupons (of their already "discounted" deal prices) pretty regularly. But what makes their coupon today (code "SALE3" for 20% off) particularly good is that you can combine it with a better-than-usual shopping portal discount. It isn't uncommon to see 6-10% Groupon shopping portal discounts, but today ShopAtHome.com is running a 3x promo, turning their usual 6% cash back at Groupon into 18%.
As an example, IF you were to find a $10 for $20 Groupon deal that was attractive to you, you could use the "SALE3" coupon (max one per transaction, up to 3 transactions per Groupon account - so if you want more than one deal, but them in separate transactions!) to reduce the price from $10 to $8. And if you navigate to Groupon via the ShopAtHome portal (after signing up for a SaH account - if you don't have one already), you will earn 18% cash back on the $8, or $1.44. Thus, you would be effectively spending $6.56 for a $20 voucher to your merchant of choice. So you'd be getting nearly 35% off the $10 (pre-coupon, pre-portal) price, and nearly 70% off the full $20 voucher price.
To calculate your after-coupon, after-portal price, just multiply 0.656 times the pre-coupon price you see listed at Groupon.
Here's some local Portland deals that look particularly interesting to me (tip: don't follow my direct links here - shop via the SaH portal, and then type in your own search in the Groupon search field) ...
Portland Prime Steakhouse (Downtown) - $50 for $25 (or $16.40)
By Design Pizza (Cascade Station near PDX) - $30 for $18 (or $11.81)
Charley's Subs (Clackamas Mall) - $12 for $6 (or $3.94)
Ben & Jerry's Ice Cream (in NW Portland) - $20 for $12 (or $7.87)
Mama Mini's (donuts in Happy Valley) - $18 for $30 (or $11.81)
If you aren't in the Portland area (or even if you are), just plug in your zip code at the top of Groupon's website and look for "local" (dining, spa services, etc.) deals that look of interest to you!