As long as you can show a significant change in a name or trademark, they cant touch you.
However, they can and do try, and defending against that takes time and money. I just came across this while browsing fark:
http://www.wsatoday.com/industry-news/industry-news/american-eagle-outfitters-sues-payless.html
"Clothing and footwear retailer American Eagle Outfitters, Inc. filed a lawsuit against Payless ShoeSource, Inc. over Payless' newest footwear collection, American Eagle. American Eagle Outfitters believes the similar name produces confusion for its consumers."