You get the idea!
Mint's icon theme Mint-X was created from two other icon themes, Elementary (folders and devices) and Faenza (applications and everything else). Since Mint-X was put together for Mint 10 more than a year ago Faenza has been steadily updated with dozens of icons added or remade and Mint-X has not benefited from these updates. Mint-Xtra is simply Mint-X brought up to date, plus a bit of cleaning up and added icons for Mint programs (mintnanny, mintupload, mintbackup, mintinstall and mintupdate) which currently sport their own conspicuously out-of-place icons. The panel icons are now symbolic and follow the panel colour scheme, so Mint-Xtra works for both light and dark panels.
New icons include:
If anyone wants to try it out, please report any bug or quirk in here so I can fix it! Also, tthe Mint apps icons could do with a more professional touch so if there's an inkscape geek out there with ideas for improvements I'm all earsamazon-mp3-store
Installation: extract the downloaded tar.gz and move the Mint-Xtra folder into usr/share/icons/ as shown
Select it with Advanced Settings under the Theme tab.
P.S: I hope the name is not a problem - I intend to propose a merge with mint-x after a period of testing (if there isn't a brand new icon theme for Mint in the works for Mint 13).