Yeah, mine was in that same shipment group from China, so I'm expecting to the the little beauty sometime this morning.
For me memory and storage space were easy decisions.
My current MBP's (mid 2009) bottleneck seems to be memory. Even maxed out at 8GB it struggles. I'm a web developer, so I have lots of apps open at the same time, primarily Photoshop, Dreamweaver, Aperture and various browsers. Safari seems to be the worst memory hog offender but I use it lots. There's normally not enough left of the 8GB for me to run Parallels too. For it to have enough memory to run decently I need to shut down other stuff.
When I got the 2009 MBP it ran just fine with 4GB of memory. As my needs grew and as applications' appetite grew for memory I was able to extend the machine's usability by doubling its memory. Currently doing that with the rMBP doesn't look very feasible.
For storage I'm currently using around 250 GB, so I knew 256 GB wasn't going to cut it. Although my storage space needs have increased in the last 3 years, it's been a slow and gradual increase. I doubt I'll need anywhere near double the space in the next 3-5 years, so to max out the SSD would have been a waste.
I see Apple's shipping estimates for rMBP's are now down to 2-3 weeks in the US for all configurations.
Countdown to kickoff.