Overstock was one of the first online retailers to enable payment by Bitcoin.
They've now announced a partnership with Shapeshift, allowing users to pay using altcoins via Shapeshift's API:
Here is Shapeshift's announcement:
And here is Fortune saying you should be able to pay with about 40 alts:
As Steem is on the Shapeshift API, I presume we should be able to use the new service to buy stuff on Overstock with Steem.