I don't think a non-rectangular edge is bad, it's just the one you have there is so random and erratic. Looks like you made a shape with scissors. The rest of it I quite like.
And I think it all depends. Cabulb's sigs are so wild and packed that a uniquely shaped border would send it over the top. ^^ For me, I experiment mostly, and try not to fall into a cycle of using the same exact style for everything I make. Although I always give it depth, using transparency.