Your command to apt-get update will refresh the package list with the latest available in the Ubuntu distro that you are using (I'm assuming your on 13.04 or 12.04.3 right?). If your are curious about what version apt-get will install, use the following:
sudo apt-cache show arduino
or;
sudo apt-cache show eclipse
It will produce the following output:
Package: eclipse
Priority: optional
Section: universe/devel
Installed-Size: 121
Maintainer: Ubuntu Developers
Original-Maintainer: Debian Orbital Alignment Team
Architecture: all
Version: 3.8.1-1ubuntu1
Depends: eclipse-jdt (>= 3.8.1-1ubuntu1), eclipse-pde (>= 3.8.1-1ubuntu1)
Filename: pool/universe/e/eclipse/eclipse_3.8.1-1ubuntu1_all.deb
...
Trust this helps!