Version 6.0 or Squeeze was released on February 6, 2011.
The ending of support for Lenny is standard Debian policy - support for a release ends one year after the next release. A year is considered sufficient time for users to upgrade to the new release.
For the most part, upgrading Debian is a painless task with it having, arguably, the best software management tools of any GNU/Linux distribution.
Debian has by far the most ports of any distribution. Squeeze supports nine architectures - 32-bit PC / Intel IA-32 (i386), 64-bit PC/Intel EM64T/x86-64 (amd64), Motorola/IBM PowerPC (powerpc), Sun Oracle SPARC (sparc), MIPS (mips (big-endian) and mipsel (little-endian), Intel Itanium (ia64), IBM S/390 (s390), and ARM EABI (armel).
Additionally, there are two ports to the BSD kernel - Debian GNU/kFreeBSD for the 32-bit PC ("kfreebsd-i386") and the 64-bit PC ("kfreebsd-amd64").
Debian is made up entirely of volunteers and was set up in 1993.