Ubuntu never was a stable distribution. Maybe it's stable by Windows standards but with the exception of the last LTS release each Ubuntu release was forked off Debian Unstable and been given only two or so months for bugfixing. Nobody – especially a distributor with only a handful of actual developers – can do wonders of stabilizing a whole distribution in that short time.
To put it into perspective:
Fedora has a very similar development timeline to Ubuntu.
Fedora 12 was released in November 2009. Red Hat Enterprise Linux (which is based on Fedora 12) was given an additional stabilization period of 12 months!