Ok, so I have a .com which is a health site/self-growth site...however, a few months later, a .net version of my dotcom name shows up. Someone with a similar name (on a .net) and made a adult site (as a hypothetical example), can I do anything about it? Or, should I not worry about it?
If the domain name isn't a trademark, there's nothing you can do about it. And I really don't think it's worth worrying about in any case. For many years www.whitehouse.com was a porn site (now just parking) and the whitehouse.gov people were unable to do anything.
is the name of your domain name generic? if not , would you spend cash to trademark it? leave the .net alone and enjoy your .com next time when you want something "big" register both .com and .net to be sure