I'm not one to criticize but damn... this has gotta be some of the most flawed logic I've ever seen on this board.
For anyone to purchase on Overstock or any other retailer they had to get Bitcoins first.. increasing the demand!
The more merchants taking Bitcoin the more valuable it is in the short-term, long-term, and anywhere in-between.
Well, I don't think you'll have many people buy bitcoin on coinbase, then go buy stuff on overstock. Likely you'll see people with big bitcoin hoards buy stuff that they wouldn't have otherwise (since it's so easy to impulse buy with it)
In the long term, of course, it's obviously good for bitcoin. For one thing it makes all the "bitcoin is a scam" people look ridiculous if it's something you can use on major online retailers.