Unregistered Trademarks,Infringement & Online Use

Hey everyone thanks for reading this post, it's my first in a looong time. I have a query about trademarks and domain name use. Here goes:

If I have developed a trademark but have not registered it yet...is it safe to use online as a domain name? I have done the "poor man trademark" by mailing all the information to myself via registered mail a while back. I own both .net and .com domains. Now what I would like to do is develop my brand via social networking sites and blogs. I will want to use the name as: wwwdomaincomslashmytrademarknamehere on several social networking websites. Until I have the capital to go ahead and trademark and build the websites I want to go ahead with publishing the idea and creating buzz possibly to even gain donations or investors via the website. All I want to do is ensure my idea concept is safe because of the fact I have obviously registered the major domains and sent myself the sealed document via USPS. Even sending myself email seems a viable way to prove that I am the originator. Any helpful advice in this arena will be greatly appreciated!