Here's an easy way to install drush without PEAR.

Note, replace the wget argument with a current version of drush. http://drupal.org/project/drush

# cd /usr/local/share/
# wget http://ftp.drupal.org/files/projects/drush-x.x-x.x.tar.gz
# tar -zxvf drush-7.x-5.7.tar.gz 
# rm tar -zxvf drush-7.x-5.7.tar.gz
# chmod a+x drush/drush
# ln -s /usr/local/share/drush/drush /usr/local/bin/drush

When you want to update drush, simply replace the drush directory in /usr/local/share.