Walmart recently introduced free shipping for customers who purchase at least $35 worth of stuff. This undercut Amazon, whose price floor was $49 for free shipping for non-Prime members.
Amazon has responded. They lowered the floor back to $35.
Walmart still has one edge, though: their free shipping is of the 2-day variety for all customers, and Amazon only offers free 2-day shipping for Prime members.
I'm encouraged that Walmart seems serious about competing with Amazon in the online retail space. I'm equally encouraged by Amazon's response to Walmart's moves. These sorts of things are what make for a healthy marketplace, and the customers are the real winners.