Lenny will be the next stable release after Debian Etch. It has today still the status unstable, but worked for me without any issues in a virtual machine on my mac.
Read it here
Upgrade worked for my without any major issues within a couple of minutes. However mySQL will not start properly and Apache2 will reset your may-be redirect commands (e.g. AllowOverride All to AllowOverride None in apache2.conf or httpd.conf). Please correct the Apache2 conf files and restart your server with /etc/init.d/apache2 restart.