Rules are important. If we don’t have them the world turns to chaos, but knowing when it is OK to break them is important. You certainly don’t break rules that define things as black and white as a limerick, sonnet or haiku. I quote, “Each form of poetry is unique to the culture from which it comes and features rules that must be followed.”, from: http://www.ehow.com/how_4814105_write-limerick-diamond-haiku-poem.html

The Rules of Poetry
http://www.creativity-portal.com/bc/bruce.price/rules-poetry.html

But, just to satisfy you and other serial rule-breakers, there’s this: http://www.ruf.rice.edu/~bioslabs/tools/report/wrules.html
And for those who need to justify to themselves that they actually can write poetry no matter what others say, there’s this http://gottabook.blogspot.com/2006/04/rules-of-poetry.html

Enjoy