A couple posts ago I wrote about how agent/editor blogs can confuse authors because of all the different and sometimes opposing advice they offer.
Jessica Faust at BookEnds has just written an excellent entry on the subject of rules and writing and stuff like that today. And she basically says what I've said, you have to take what works for you, don't try to be all things to all people, and to most importantly be thoughtful and professional. However, she not only writes more in depth about the whole subject, but she's also an agent so has more of an inside scoop than I ever will.
If you have the inclination, check it out!