I realize that I have read a series that would be considered "poly". Laurell K. Hamilton writes supernatural romance stuff and has an ongoing relationship with many, many men throughout the series. At one point she is living in a triad while seriously dating one other man, it gets rather complicated
The series starts off with a pretty good plot, if you dig the whole vampire/supernatural thing, but I found that the plot became very, very thin later in the series and was pretty much porn with loose character development thrown in. Definitely poly though!