If you were thinking of computer networks where Ethernet is used as a computer to computer interconnect or NAS type of setups, then those are the MINORITY. And if you do need this functionality, there's always a relatively cheap adapter that is 100% compatible.
And that eats one of your very useful Thunderbolt ports. With the other used for Firewire, leaving zero for display (and HDMI can't do high-res displays).
Thing is... Yeah, this is all "minority" functionality, but you know what? The point of the Macbook Pro was to be the machine which has the extra features that only a minority of users need, or that they only need a minority of the time.
Also, before you are too quick to condemn the Ethernet port as redundant, please do a quick test: Get 750GB of files. Now run a full (not just incremental) backup to a Time Capsule over gigabit ethernet, and run another backup to it over 802.11. Let us know how equivalent they are.
Nothing's really changed much since this thread was first posted; I still find that the cMBP is a much more powerful computer. I bought a Mini, and I am using the firewire port on it -- in fact, I wish it had two, because I want to use both FW800 and FW400 devices, and I want to be able to leave the 400 plugged in but possibly remove the 800. I bought a new drive with FireWire interfaces on it last night, because it turns out I still use those, because they're still awesome for disk transfer.
I still think it says a lot that people were dismissing my concerns about the rMBP by saying that "only professional users" would want that functionality.
Maybe a year or two out, there'll be thunderbolt hubs that have dual-link DVI (or just displayport) output, ethernet, firewire, and all the other stuff that's missing. But in the mean time... This is just the thing where some Apple fans are so devoted that they will actively attack functionality that's not included in a given Apple product on the grounds that they can't emotionally handle the idea that an Apple product could not meet the needs of absolutely all users unless the users are somehow defective.
Still loving the OS, still buying Macs, but also getting more concerned about the long-term viability of OS X as a primary platform for my work, because Apple seems to be moving away from the stuff I need...