Brand Name NOT Trademarked in Domain Name

Hi, I'm well aware that it's not a good idea to put a trademarked site's name as your own domain name- but what if the brand name hasn't been trademarked? what if i take the established site's .com name and start my own .net site? could i still be sued somehow?

yes. happened to me. They wanted to sue me once I came to spot No.2 on Google when you search their name (which was also my name, but apparently they started their site before me. We were both .COM). Their site was first, my was second and their Twitter was 3rd place.