Here's a line you can add to your .bashrc (or other resource script) that will try an "svn update" on all the subdirectories of the current directory:
alias svn_upd_all='find . -type d | grep -v "/.*/" | sed -e "s/ /\\\\ /g" | xargs svn update'
To use, open a Terminal and navigate to the top-level directory (such as your Eclipse workspace directory), then type the following:
Although it will try to update non-Subversion directories, they will be skipped.