I know, I know - replying to your own post is bad....
For the benefit of the Samsung Galaxy Tab 7.7 owners who uses an Ubuntu Linux 12.04 (or Linux Mint 13) PC and wishes to transfer files between these two, I am listing several possible solutions here. FYI, using USB is totally out of the question - IT WILL NOT WORK! - at least for the moment, that is, until Samsung or Canonical does something about it.
The possible solutions (and comments) are:
a) remove SD card from Samsung, plug it into a card reader recognized by Ubuntu 12.04 and move/copy the files (Comment: very 'fussy' and clumsy).
b) use Bluetooth to move/copy files (Comment: very slow).
c) use the Airdroid utility to move/copy files (Comment: OK but fails sometimes).
d) use the 'FTP Server' utility to move/copy files (Comment: fast - best solution so far).
Note that the 'Airdroid' and 'FTP Server' utilities can be downloaded & installed from Google Market (or Google Play as it is called now). They are both free apps - so they are extremely good value for the (zero) money.