So far, the following systems have been confirmed as vulnerable:
Ubuntu Linux 64-bit ( 10.04, 10.10, 11.04, 11.10, 12.04 ) ( via many including @michealc )
OpenSuSE 12.1 64-bit MySQL 5.5.23-log ( via @michealc )
Debian Unstable 64-bit 5.5.23-2 ( via @derickr )
Fedora ( via hexed and confirmed by Red Hat )
Arch Linux (unspecified version)
Feedback so far indicates the following platforms are NOT vulnerable:
Official builds from MySQL and MariaDB (including Windows)
Red Hat Enterprise Linux 4, 5, and 6 (confirmed by Red Hat)
CentOS using official RHEL rpms
Ubuntu Linux 32-bit (10.04, 11.10, 12.04, likely all)
Debian Linux 6.0.3 64-bit (Version 14.14 Distrib 5.5.18)
Debian Linux lenny 32-bit 5.0.51a-24+lenny5 ( via @matthewbloch )
Debian Linux lenny 64-bit 5.0.51a-24+lenny5 ( via @matthewbloch )
Debian Linux lenny 64-bit 5.1.51-1-log ( via @matthewbloch )
Debian Linux squeeze 64-bit 5.1.49-3-log ( via @matthewbloch )
Debian Linux squeeze 32-bit 5.1.61-0+squeeze1 ( via @matthewbloch )
Debian Linux squeeze 64-bit 5.1.61-0+squeeze1 ( via @matthewbloch )
Gentoo 64-bit 5.1.62-r1 ( via @twit4c )
SuSE 9.3 i586 MySQL 4.1.10a ( via @twit4c )
OpenIndiana oi_151a4 5.1.37 ( via @TamberP )
FreeBSD 64-bit (many versions)
Most Linux vendors should have a patch out soon, if not already.