As a mac user I won't be buying one
As a professional web designer I have to say I won't be "upgrading" to the retina display laptop. My current setup (2 year old MBP 15 with hi-res display) has a 128gb SSD. I seem to spend my life moving stuff off the internal disk just so Photoshop stops telling me its scratch disk is full (I thought I was done seeing that alert 14 years ago). I don't use iTunes to store music, or iPhoto for images because it'll be too big a hit to the storage. I've got CS3 and Windows 7 running in Parallels; that leaves me with a whopping 9gb of free space. If it gets too painful I'll end up ripping out the SSD and going back to a standard drive, doesn't look like that'd be an option in this new one though.
As for the RAM; I've never not stuck in an upgrade a year or so after the initial purchase. Not impressed with the "just buy the fully specced version" comments. Can I also buy some glasses that'll allow me to see through time too? AppleCare is all well and good but being 1.5 hours away from an Apple store that would turn a quick five minute job of upgrading the RAM into a tedious, previously unneeded trip.
I can see the thunderbolt port being useful, but the lack of included adapters with a high-end system is a disgrace.
The negatives far outweigh the positives for me to consider this. Whilst I'd stomach these things on the Air that machine is clearly meant as a satellite to your main setup, I'm not prepared to accept them on what would likely be my only machine.