There are many good projects and services out there that scare/annoy away potential users by whacking a "register or login" box in their face just before things get interesting.

My identity isn't "free" and managing yet another account comes with a burden (another password to remember or store somewhere, another security risk).

Whoever thought that creating pipes (i.e. experimenting) without logging in was somehow detrimental to Yahoo's business interests(?), had things backwards.