Yesterday I did a 'do-release-upgrade' from my laptop (HP DV-6) running flawlessly Kubuntu 12.10, to 13.04. Upgrade process ended up with no errors.
But now, when laptop boots normally, hangs during graphical login. Sounds it has some issue when enabling network interfaces, since they are not working at all while at the boot prompt.
Alternatively, if I start in recovery mode, and choose "resume" in the first choice list, it boots up, logins, and works normally, with working network too. Can't understand the differences between two boot options so as to compromise the functionality of the system...
I also upgrade my desktop computer (a quad-core AMD based PC) from 12.10 to 13.04, with no issues at all.