Ethernet Port: Don't need
Optical Drive: Don't need, but took my old one out to make room for a hard drive in my previous MBP and put it in a case so I have it if I need it. Haven't actually used it since (about two years ago).
17" was always too big for me to lug around, always preferred the 15" (and always upgraded display to get more resolution which is not needed with retina). For me 15" is the right combination of screen real-estate and size.
And I actually appreciate the slimmer design and lighter profile. It's noticeable over my almost 5 year old MBP that I'm upgrading from.
My only lament is that I wish everything wasn't soldered in so I could replace/upgrade it myself, but that's not just an Apple problem, most laptops are going that way in the name of decreasing size.
I'm pretty happy with this new kit actually, but I've only used it for a few days thus far.