Here's what the Design Challenge T&Cs says about where to blog:
"Post to the Competition Site blogs on the progress of their Project (Blogs) not less frequently than once per week during the Competition Period. One or two weekly omissions are permissible as long as the total number of Blogs is at least 10."
The competition site is element14, not your personal blog (e.g., blogspot)
Randall Scasny
Design Challenge Team