An interesting blog post:
http://www.carlopescio.com/2011/04/your-coding-conventions-are-hurting-you.html
For me, the most important point is that when a class is starting to get too large, you shouldn’t just cut and paste a load of methods to a similarly named helper class. Rather, you should think carefully about how the object should be decomposed into smaller objects, each of which is correctly encapsulated and has methods appropriate to it.