I just find this all to be very curious... because I feel it's hard enough to find ONE person with whom I connect, and especially find another couple with whom my husband will find the wife attractive or connect with her. To me, dating another couple would feel too much like "swinging" or "wife swapping" (of which I am not opposed, it just has no interest for me) and I'd rather have my own relationships.
A huge reason as to why I am poly, is that it allows me to branch BEYOND my husband and create my own relationships and connections... if we were to "share" another couple (even if that meant me being with the man and him being with the woman), it would just feel like a continuation of our marriage.
I don't have anything against couples who date couples... just curious as to whether people have had success in it. I totally can see why a single might want a couple... more people to love and share the connection with - just having a hard time wrapping my head around couples with couples?
However, these have been some great answers!