There's always 2 things to watch for when a new merchant jumps on the bandwagon:
1. Are they using a 3rd party processor?
2. Are they advertising it on their homepage? Now the Tigerdirect.com one is absolutely huge. But is Tigerdirect.com get less traffic than Overstock? But if you don't take the time to understand the refund policies, you may just stick with credit card if you're not interested in BTC.
Frankly don't see why any major merchant would NOT use 3rd party processor right now? They can't pay their suppliers with BTC, and unless they're a bank they're not in the business of currency exchange. It's not their core business so why would they take on additional liability/risk of holding on to BTC? That wouldn't fly well with stock holders either.
That would be the typical business way of thinking. But I'm hoping there are some businesses who will think outside of the box and take that risk eventually. Find suppliers who are also willing to take BTC. Then use that as a marketing strategy for themselves and BTC. Of course merchants accepting BTC at the POS is still a step in the right direction.