MacTeX-2010 installs updated versions of the GUI applications that were already in MacTeX-2009.
MacTeX has optional packages to install two font collections (Latin Modern and TeX Gyre) in /Library/Fonts; these TeX fonts are already in TeX Live, but installing them in /Library/Fonts makes them available to standard Macintosh applications like Adobe Illustrator. By default, these fonts are not installed.
MacTeX installs the latest version of Ghostscript, 8.71, and an updated “Convert” from ImageMagick 6.6.1. These packages are self-contained; MacTeX installs no libraries in /usr/local/lib.