A couple things I have learned or observations I have made since hanging out on this board.
Poly is HARD work
Poly is NOT a way to accomodate a cheating spouse
If you are currently in a mono marriage - make sure your marriage is SOLID before adding additional partners. Spend some time working on learning to communicate better as it will be even more important later on.
The original spouse/partner will have feelings of jealousy in some form in the beginning, while there is NRE between the other and the new addition
No one has it all figured out
Set boundries - don't expect your partner to just know what lines can't be crossed