I love the idea of this thread as well! I hope more people with mixed breeds chime in soon. 
These are my 3 mixed-breed girls (Cayuga mom, Rouen dad):
When I wanted to start a small flock of ducks here, it was very difficult to find any at all. I had to order Cayuga duck eggs and have them shipped from southern Sweden. Out of a total of 24 eggs, I got two female Cayugas that hatched successfully. Needless to say, I will never do shipped eggs again. Very sad experience (and expensive!). I then found an ad posted by a lady who lived not too far from me who had a couple of male ducklings for sale. I ended up bringing one home, he was a Rouen. The following Spring (last year) I stuck 8 of their eggs in my incubator and all 8 hatched! I kept the above 3 females and sold the rest since I wanted to keep my flock fairly small. I love my sweet mixed-breed girls! And they are excellent layers! They started laying in January this year and just stopped last week.

These are my 3 mixed-breed girls (Cayuga mom, Rouen dad):
When I wanted to start a small flock of ducks here, it was very difficult to find any at all. I had to order Cayuga duck eggs and have them shipped from southern Sweden. Out of a total of 24 eggs, I got two female Cayugas that hatched successfully. Needless to say, I will never do shipped eggs again. Very sad experience (and expensive!). I then found an ad posted by a lady who lived not too far from me who had a couple of male ducklings for sale. I ended up bringing one home, he was a Rouen. The following Spring (last year) I stuck 8 of their eggs in my incubator and all 8 hatched! I kept the above 3 females and sold the rest since I wanted to keep my flock fairly small. I love my sweet mixed-breed girls! And they are excellent layers! They started laying in January this year and just stopped last week.
Hens go broody when you don’t want them to… and won’t go broody when you do.
But, I'm culling the silver drake and instead getting a Rouen drake and hen, and two WHs. :/ Keeping the silver mixed breed for sure, but the demand for ducklings in my part of the country is so high for pure breeds, I am keeping mostly pure breeds. Might hatch a few RouenxWH for cute layers though!