upgrading the hard drive or flash memory

Yes, it is very very difficult to repair or upgrade. See link:

http://ifixit.org/2753/macbook-pro-with-retina-display-teardown/#more-2753

 

The RAM is soldered on, however, the SSD is removable but at the moment there are no replacements available. Third party companies are in the process of making these replacements though.

 

Non-retina 13" and 15" MBP, 2012:

RAM is user upgradeable.
HDD is user upgradeable.
Battery is not considered user replaceable by Apple but you can remove it with the right screwdrivers.

Retina 15" MBP:

RAM is not upgradeable, physically soldered in.
SSD/Flash is not considered user replaceable by Apple, but it's a small board that can easily be replaced if someone starts offering replacements.
You need a special screwdriver (pentalobe) to take off the bottom. It isn't glued shut.
The battery is not replaceable (glued into case).

 

That was the best news I read all day! I even went to the iFixIt site to check it out myself. I'm not kicking myself as much for ordering the 256GB version of the rMBP now. I simply could not afford all the extra cash even though I upgraded the RAM to 16GB on the base model. As the RAM is not replaceable, it seems we're just forced into going for the max offering...